I'm seeing this behavior with IBM's Rational Software Architect on Gutsy AMD64. It looks like the issue is the same, but it's not from the 64-bit libgtk2. Instead, it's from the 32-bit libgtk2 installed by the ia32-libs package. I'm going to patch and rebuild and see if that fixes it. Unfortunately, the ia32-libs package is almost 400MB of source code, so it's going to take a while to rebuild and test.
I'm seeing this behavior with IBM's Rational Software Architect on Gutsy AMD64. It looks like the issue is the same, but it's not from the 64-bit libgtk2. Instead, it's from the 32-bit libgtk2 installed by the ia32-libs package. I'm going to patch and rebuild and see if that fixes it. Unfortunately, the ia32-libs package is almost 400MB of source code, so it's going to take a while to rebuild and test.