I can confirm this issue with the manpage included in apport 2.17.2-0ubuntu1.1 on Ubuntu 15.04. Note that the manpage do mention apport-cli under options, and it looks like ubuntu-bug accepts the same options. These are documented in apport-cli, but this should be clarified somehow for those reading the manpage. This is also touched upon in bug 1395307 though.
However, even the apport-cli manpage doesn't mention the "--tag" option, which should probably be documented somewhere. (It does mention -p though)
Thanks for reporting.
I can confirm this issue with the manpage included in apport 2.17.2-0ubuntu1.1 on Ubuntu 15.04. Note that the manpage do mention apport-cli under options, and it looks like ubuntu-bug accepts the same options. These are documented in apport-cli, but this should be clarified somehow for those reading the manpage. This is also touched upon in bug 1395307 though.
However, even the apport-cli manpage doesn't mention the "--tag" option, which should probably be documented somewhere. (It does mention -p though)