Another workaround to this annoying issue can sometimes be to do a scripted export where the filepath is set to a variable.
What happens if you select 'Hide extension'?
If you click the "Hide Extension" button it only "hides" the extension. It still appends the .tab extension to the filename. Very frustrating.
Thanks Douglas. I can confirm this behavior of FileMaker 12 on OS X Snow Leopard as well:
Thank you for your post.
I was able to confirm this issue on my 10.7.4 machine. I forwarded your report to Development and Testing for review.