Decrypting attachments

No one answered this:

Under Windows7 and TB 3.0.1, if I get an encrypted attachment, I get two
choices: "decrypt and open" and "decrypt and save". The former never
works, I think because windows does not know what to open the file with.
How do I specify this in enigmail? If I can't, this must be a bug in enigmail.

Thanks,
Jim