Unknown revision numbers in bzr tags command

When I run the bzr tags command on a branch, I often get some tags that are displayed with no revision number. It appears as a question mark. For example, when I run this command:

bzr tags -d lp:~zaber/openobject-client/main

tag 5.0.7 doesn't have a revision number:

5.0.0                930                                                       
5.0.0-2              933
5.0.0-3              938
5.0.0-alpha          719
5.0.0-rc1            771
5.0.0-rc1.1          776
5.0.0-rc2            830
5.0.0-rc3            858
5.0.1                946.1.19
5.0.2                976
5.0.3                983
5.0.4                986
5.0.5                993
5.0.6                1000
5.0.7                ?
5.0.7rc1             1022
5.0.7rc2             1042

This may happen more often when I've got shared repositories for several local branches, but I'm not sure.

Solution

Those tags are known to bzr (fetched or merged from another branch in some pull or merge operation) but corresponding revision is not present in your history (not merged to your branch).

Strictly to say that's a bug, you can find it in the bzr bugtracker on Launchpad.net.

What you can do about such tags:

remove them from your branch only with bzr tag --delete XXX
use them to merge those revisions later with bzr merge -r tag:YYY lp:XXX
look at the corresponding revision ids with bzr tags --show-ids