I have the same problem, also on Slack 9.1.
A few things I have discovered:
-While the graphical system monitor is behaving as described in the above post, top is reporting both memory and swap usage just fine. Thus, in the meantime my suggestion is to just use top for resource monitoring.
-Take a look at the follwing:
I am not at home right now, but I'm gonna try this once I'm home (in about 5-6 hours) and see if I come up with anything.
Anybody else have any ideas?