There have been several other reports here of this occurring over the past few years. Here's one of the threads I found, but says it applies to E170/E175's and not CRJ/CR7/CR9. I think there are some more out there --

http://www.flyertalk.com/forum/delta...-e175-dtw.html

Not sure of the actual policy, but it does not seem consistently enforced if it is.