The bug was present in 1.6.3, but it seems to have been fixed in 1.6.3ubuntu0.1.
If you roll back to 1.6.3, it's easy to reproduce it:
$ PAGER=
$ apt changelog apt
It shows this error message:
usage: which [-as] program ...
and then goes on to show the changelog for apt.
Whether apt called which or not, it was a bug nonetheless. The changelog for apt doesn't mention fixing this, but it has been fixed because it cannot be reproduced on 1.6.3ubuntu0.1
The bug was present in 1.6.3, but it seems to have been fixed in 1.6.3ubuntu0.1.
If you roll back to 1.6.3, it's easy to reproduce it:
$ PAGER=
$ apt changelog apt
It shows this error message:
usage: which [-as] program ...
and then goes on to show the changelog for apt.
Whether apt called which or not, it was a bug nonetheless. The changelog for apt doesn't mention fixing this, but it has been fixed because it cannot be reproduced on 1.6.3ubuntu0.1