Thanks for your reply.
Well, that gave the sidebar a min-weight, but it didn't prevent the mainbody from taking too much space at the bottom.
I solved by applying your suggestion to div#t3-content instead like this:
div#t3-content {
min-height: auto!important
}
That seems ok for now, I'll check that it doesn't cause any issue elsewhere.
Thanks,
have a good day.