Accepting that BCC + PGP is a very ... awkward use situation.
After resolving recipient/key issues that resulted in errors, that sending again would result in the expected (and displayed) encryption settings. Instead, even though the "encrypt" button was highlighted, the email sent in the clear (please see attached screenshot of the email at step 6 below; it will send unencrypted upon pressing send.)
Steps to reproduce:
1) Compose new email with one to: recipient and at least one bcc: recipient. One of the recipients of the email need to have a key not known to enigmail or have multiple valid keys (e.g. it will trigger user input for key selection)
2) Select Encrypt (during testing, I also had sign selected)
3) Press send; receive standard bcc warning dialog ("The message has BCC (blind copy) recipients..."). Select "Encrypt normally"
4) Receive error: "Internal Error: promised encryption disabled"
5) Select "Cancel" (only other option is "send message unencrypted") (This is perhaps a lower priority bug itself - ideal option is present key selection dialog, allow user to resolve question, proceed with encryption)
6) Return to message (to "fix" issue) - both the "encrypt" and "sign" buttons are still highlighted. Message is shown as signed (in-line text)
7) Press "send" again; message sends "as-is" - signed, but not encrypted, with no further user interaction.
This may be partially related to some of the behavior in https://sourceforge.net/p/enigmail/bugs/473/
OS: Linux 3.13.0-79-generic #123-Ubuntu (Ubuntu 14.04 LTS)
Please ping me for further testing / logfiles / etc.
I can not reproduce this using Enigmail 1.9. Behaviour at point 7 is not sending, but instead jumping to 3.
Would you mind upgrading and test if this issue is fixed for you, too?
Just a quick warning: Enigmail 1.9 requires GnuPG version 2.x - this may introduce additional installation effort for you.
Thanks for the fast response!
I experience a similar behavior still with 1.9 - an interesting change is that signing also does not take place after step 4; yet both the encrypt and sign buttons display an "on" state.
I can send logs and screencasts (privately) if that would be a useful next step.
I can't reproduce this anymore.