Locked out from random heroics.

Hello everyone!
Me and my mates recently started playing here on Icecrown, and just got to the point of running rhcs.
We had a weird thing happen yesterday, where we were locked out from all of the dungeons, and could not join anymore for that day.
Don't remember this being a thing from WotLK before, so I wanted to ask, is this intentional?
We also had some lockouts that were unique, for example I wasn't locked out of Ahn'Kahet and Nexus, one guy was in all the dungeons on heroic that day, and one was not locked out for a different one. Question is, could this affect queueing for randoms, or was this a bug?
Thanks in advance!

There is no bug regarding the lockouts.
1. One account can only enter 5 instances(dungeons/raids) per hour. After the fifth, you need to wait until 1 hour passes from the point of entering the first one.
2. Every heroic dungeon can only be done once per day. If the group consists of people with multiple different lockouts, you will only be able to enter the dungeons to which NONE of the party members are locked. The best way to "spam heroics" is by grouping up and queuing together, so as to have everyone on the same dungeon lockouts. If you queue for random dungeons, the account-wide lockout shouldn't affect you as each dungeon takes about 10-15(20 if Culling of Stratholm) minutes to complete(less if group is blasting).