simple check of event.isCancelled() & Material.AIR should do the trick.

Wait, if this is ought to fix the behaviour of WXT not caring about block replacements, then I suggest adding a config option regarding this. I like that we admins can mod the gates a bit more through WorldEdit (especially with /repl).

Anything i add is normally configureable. In this case i was more speaking of using repl on the gate sign.