I use Pro Animator and render to .mov files (PNG / Million Color +) all the time. Occasionally save single frame .tga files. I have never seen the extension you mention. You may want to check that your anti-virus software or some other memory resident detection program is not doing it due to something it is detecting.
2 - Better QuickTime movie flattening. Some people were getting a *6 error when rendering movies. This was caused by a new version of QuickTime. A change has been made to make QuickTime movies cross-platform and more reliable. It also gets rid of the problem on Windows where extra #res files were being created.