Files encrypted with gpgex set the PLAINTEXT packet to a ??temporary?? file
descriptor. When you decrypt the file with gpg itself and status fd you see the
following:

[GNUPG:] PLAINTEXT 62 1268210582 -&12

notice "-&12". It has been established by 3rd party clients like PGP Desktop,
Universal and other Gateways - to use the PLAINTEXT packet information as the
original filename instead of the one currently attached to an e-mail.

What happends when this message wents through a decryption application is, that
it gets automatically renamed from myfile.pgp to -&12

The Plaintext packet is used to reveal the original unencrypted filename,
because some 3rd party application use this extension to obfuscate the original
file. I.e. when i encrypt file.doc it becomes <somerandomstring>.pgp - the
information that the original file was file.doc is stored in the plaintext
packet. When you now attach this file, encrypted with GPGEX to an e-mail message

• the misbehaviour with other 3rdparty applications occur.

Two Solutions:

Either do not set the plaintext packet at all
OR
Set the filename correctly (im guessing gpgex is using command line gpg and
piping the input?) in this case - use the original filename as a parameter for
--encrypt instead of the temporary filename/descriptor.