Does this help? With debug on error I get two hidden buffers:

*epg* contains:

Process epg exited abnormally with code 2
[GNUPG:] NEED_PASSPHRASE_SYM 9 3 2
[GNUPG:] PINENTRY_LAUNCHED 10719 curses 1.1.0 - dumb :0
[GNUPG:] ERROR get_passphrase 32870
[GNUPG:] CANCELED_BY_USER
[GNUPG:] FAILURE symencrypt 33554531

And *epg-error* contains:

gpg: problem with the agent: Inappropriate ioctl for device
gpg: error creating passphrase: Operation cancelled
gpg: symmetric encryption of '[stdin]' failed: Operation cancelled