User blog comment:Miskos3/Fairy Tail 530: Neo Eclipse, Review/@comment-29778526-20170409192555/@comment-7418318-20170410053858

There are several possibilities I can come up with.


 * 1) The King had the original gate dismantled as he promised Anna. Later he constructed his own gate, but they were unable to make an exact copy and thus it had some flaws.
 * 2) The gate can only enable permanent time-travel if it's opened properly with Celestial Spirit Mages stabilizing the tunnel on both ends. That didn't happen in the GMG arc and thus it could only create unstable connections through time, which became undone when the Gate was destroyed.
 * 3) The travel only becomes permanent once the tunnel is closed. When Anna came through she properly shut the gate down after closing the door, while Lucy and Yukino (as well as F-Lucy and F-Rogue) only shut the door, but the time-tunnel remained active and when the thing blew, it reversed anything that hasn't run through the proper shut-down procedure.

Personally #1 makes the most sense to me. If the second gate was an inferior/imperfect copy of the original, it would easily (and logically) explain why it or rather they work slightly differently.