I believe many people had also find out that Carsomyr's magic resistance stacks only for a short period of time for some reason/s. Is it suppose to be like that or is it a bug? If it is a bug, is there any way to solve it? Thanks in advance!

It is a bug. There is a mod that corrects it, but I can't remember which one. IIRC, the Item Upgrade Mod fixes it.

It is not a bug. The Carsomyr's resistance sets yours to 50%. It's not supposed to stack.

either way it's buggy -- because if you equip Carsomyr and then put on the Ring of Gaxx, yor Magic resistance hits around 60 or so. But if you unequip the sword even for a second, then re-equip it, the MR goes to 50 again.

Carsomyr *sets* MR to 50%, rather than adding 50% MR. People vary on whether this is a bug or intentional. If you want it to stack, an easy workaround is to equip Carsomyr first and then equip other items. If you have to re-equip Carsomyr, you'll need to re-equip your other MR items as well.

It also selectively dispels magic, another bug. Weimer's Item Upgrade fixes the dispel magic bug, but I think it leaves the MR unchanged.

@CamDawg,
I always equip Carsomyr first, and then the other magic resistances stuff. For example, I equip Carsomyr first, then an amulet of magic resistance(brought from underdark). The stats screen will show that Keldorn have 60% MR. But after a while, when I check the stats screen, it goes back to 50%(All the while, I made sure that I didn't change weapon or unequip Carsomyr). So it seems to me that since the MR(when equipping Carsomyr) can go to 60%, it don't seems to set to 50% for Carsomyr.

Hmm, I have the item upgrade mod installed... maybe it does fix the MR of Carsomyr. I'm using Keldorn with Carsomyr, and his MR is at 55% (Carsomyr and the 5% MR amulet from the Unseeing Eye). However I don't really pay close attention, so it may have rolled back to 50%. I'll check the item files when I get home and see what the item upgrade actually does to the sword.

This mod also fixes Carsomyr +5 and Carsomyr +6 so that they use the same "dispel magic" opcode as the Staff of the Magi. That is, they will actually dispel things. They also increase MR by 50% rather than setting it to 50%. From:
www.weidu.org/c2/README-ItemUpgrades.txt (http://www.weidu.org/c2/README-ItemUpgrades.txt)

You mean to say I rushed home and wasted 10 seconds opening NI for information that was in the readme? Argh. :D

You can get just the Carsomyr fix without installing the entire item upgrade mod. Download the mod and just take the sw2h10.itm file from the c2\fix folder and drop it into your BG2 override folder.

With the unmodded Carsomyr, MR will keep changing to 50% regardless of order of equipping or any other factors. This is not a bug, it is the way it is supposed to be.

@Rastor,

Since you confirmed that for me, I guess I will stick to the normal one, as I prefer to roleplay proper for my current game.

@CamDawg,
Anyway, thanks, I would have use your method if it was a bug.

Sorry to revive a dated topic, but I now have a more definitive answer for this. Kevin Dorner had corresponded with some devs over at Bioware who confirmed that Carsomyr is supposed to set MR to 50%, not add to it.
Baldurdash Carsomyr thread (http://forums.fwstudios.net/index.php?showtopic=2891&st=0&#entry48448)

Just a note for everyone,

I'm pretty sure that any inate magic resistance bonuses (i.e. from Selfishness Test, Machine of Lum the Mad, Wizard Slayer, etc.) will still be included when you equip Carsomyr.

For example, if I naturally have 15% magic resistance - i.e. without the use of any items - and I equip Carsomyr, then I have 65% magic resistance. Carsomyr won't undo your natural bonuses.

What did you mean earlier that it randomly selects times to dispel magic? It is supposed to dispel magic on each successful hit, right? I only wish I knew what level the dispel functioned as.

The original Carsomyr was encoded incorrectly, so it rarely dispelled magic on hits, even though it was supposed to.

If I'm reading the effects correctly, the dispel magic is 100% effective, although still a third level spell. Minor Globe and Globe of Invulnerability would not be dispelled, although Stoneskin, Haste, etc. should be. A mage with a Minor Globe and Stoneskin loses their Stoneskin but not their Globe. I have no idea how it interacts with spells like Spell Deflection, Spell Trap, and Spell Turning.

edit: Above is referring to the dispel on hit effect. The casting ability of dispel magic is at level 15.

But the latest patch fixed this problem? It seems it dispels magic frequently when I use it. Or is it just showing the graphic?

The one major error I remember with Carsomyr was that it dealt only 1d10+5 even though it was supposed to deal 1d12+5. I downloaded the huge set of patches off of Baldurdash.com to fix this along with a slew of other things. I thought that was the only error with Carsomyr. Have I download everything I can to make the sword work the way it is intended to?

If the dispel magic doesn't work right, what can I download to fix all of this?

I'm pretty sure that any inate magic resistance bonuses (i.e. from Selfishness Test, Machine of Lum the Mad, Wizard Slayer, etc.) will still be included when you equip Carsomyr.Correct, and it is coded correctly there.

If I'm reading the effects correctly, the dispel magic is 100% effective, although still a third level spell.100% effective? That doesn't sound right. It should work the same way as staff of the magi.

A mage with a Minor Globe and Stoneskin loses their Stoneskin but not their Globe. I have no idea how it interacts with spells like Spell Deflection, Spell Trap, and Spell Turning.Out of all the spells you just mentioned, it will only affect Stoneskin (or at least, that's how it should work.)

If the dispel magic doesn't work right, what can I download to fix all of this? Supposedly Baldurdash fixes it, although he may also change the code for the magic resistance. Bioware did the MR correctly on the sword.