Schedule Slip: They're becoming increasingly infamous for this, due to a company policy of not rejecting work. Though they're generally relied upon to fix any error on their TV release come the DVD/BD release.
Justified in the case of Puella Magi Madoka Magica. Due to certain real life events, the final two episodes airing was delayed for over a month. Gen Urobuchi, who wrote for the series, explained that the slip came as a bit of a relief because they'd been having trouble animating them. When they finally did air on April 21st, fans could see why. Shaft loves its surreal art, after all.