I'm not sure this is actually the case. What I think happens is if you use a quest scroll while another quest scroll quest has been summoned or is already in progress that new quest cannot be undertaken.

I popped in to report this bug as well, though it should be noted that the quest doesn't 'do nothing'. Instead it creates the quest icon next to your character on the map, that is not removable by any means.

I do my quest scrolls one at a time - save, buy, complete it; save, buy, find it is a dud; reload, buy, etc, etc.

I don't think the problem has anything to do with other quest activity because there is nothing quest-related going on.

Also, sometimes when I load & re-buy in the same turn, the 2nd scroll works.