It was in fact also a bug in blt's dependencies, but those seem to be less pathological in version 2.4z-4; in particular blt no longer Depends: blt-common.
** Changed in: blt (Ubuntu) Status: Rejected => Fix Released -- process_queue: Assertion `dependtry <= 4' failed. https://launchpad.net/bugs/46530 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs