Looks like it only does this:

Patch details for v1.20 English

* Added code to prevent non-NWN files from corrupting modules in the Toolset.

Read the front page of SP.

That's pretty much already. I haven't really found any bugs at all in SP after upgrading to 1.9.

@Forashi
Oh, there are bugs! Patch 1.20 was a "panic" patch for the toolset. I heard a rumor that the next patch might be here in a week or so.
(Btw, you mean 1.19, not 1.9)