bitlbee-libpurple has a versionned dependency against a bitlbee release
that is not in Debian unstable.
anarcat@curie:~(master)$ apt show bitlbee-libpurple | grep Depends
[...]
Depends: libc6 (>= 2.14), libgcrypt20 (>= 1.7.0), libglib2.0-0 (>= 2.24.0), libgnutls30 (>= 3.5.6), libpurple0 (>= 2.6.0), debianutils (>= 1.16), bitlbee-common (= 3.5.1-1)
anarcat@curie:~(master)$ rmadison bitlbee | grep unstable
bitlbee | 3.4.2-1 | unstable | source, kfreebsd-amd64, kfreebsd-i386
[...]
Therefore the bug is not, as far as I understand this, in
bitlbee-mastodon, so reassigning.
A.