In particular, I've found that calling drawImage with the negative of the source image's height fails to draw. Test cases attached.
Created attachment 68334 [details]
Negative Source Height Test Case
Created attachment 68553 [details]
Comment on attachment 68553 [details]
Clearing flags on attachment: 68553
Committed r68176: <http://trac.webkit.org/changeset/68176>
All reviewed patches have been landed. Closing bug.