XI/CMS: Per Changelist Transport

We have had CMS for XI up and running for a while. Suddenly transport of changelists has stopped working. When activating a changelist it used to go to status "Transportable". Now it goes straight to "Closed"!

When I check in XI administration web page -> Directory -> CMS Transport settings, I see that "per Changelist Transport" is set to "False" for "All directory content".

I can set it back to "True", but if I leave the browser and go back in the seetting has changed back to "False". Very frustrating.... Any ideas?

-AD