They are. There have been cases, while sporadic and infrequent, just enough to make it an issue, where the credits would not show up after checking out (or possible "check out time").
If you're planning on doing credit-based meals after check out time, it may be a good idea to stop by Guest Relations BEFORE you head to the meal, just to check and make sure everything is set. If they are "broken" they'll be able to fix them for you. If they try and claim that they expire at check out, ask for a supervisor! (There was one or two cases where that happened too)
The majority of people aren't having any issues, especially lately, but it can and sometimes does happen. So, no sense in changing stuff around, just be aware that issues have happened, and check with Guest Relations before the meal if you're concerned.