We haven't seen this problem before. On the Mac OS X 64-bit version it is very strange, but something we can assume as due to the fact that this version is still 'experimental'. However, on the rest of platforms (including the 32-bit Mac version) this kind of things should never happen.
The next version of the PixInsight Core application is being built right now based on the last version of the Qt framework (4.7.2) which fixes some bugs. Let's see if this problem goes away.