Editing the last (or unique) post does not bump it if it has been assigned (assign plugin)?

I have a topic with a single post that is updated regularly.
Since I installed the assign plugin and assigned the topic, editing the post does not appear to bump it.

The assign plugin adds what looks like a post in the topic indicating to whom and when the topic was assigned.
Does this prevent the unique “real” post from being considered the “last post” and therefore from being bumped when edited ?

If so what is the workaround to bump it ?
I tried to unassign the topic, but it merely adds yet another post “unassigned xx minutes ago”, and it does not solve the problem (no bump when enditing the only “real” post).

Try deleting the “small action post” created by the assign plugin.