I have a torrent which is set to stop seeding at a ratio of 5.0, and indeed, when that ratio was reached, it stopped.
However, if I now Pause All Transfers (from the tool bar) and then Resume All Transfers, its option is changed to "Seed Forever".
Even more oddly, sometimes (but only sometimes) it resumes seeding. Sometimes (even though it's set to Seed Forever) it doesn't resume unless I click Resume All Transfers a second time.
Martin