I think cait traps are bugged (need more feedback)

So caitlyn traps are supposed to have ennemies "become immune to Yordle Snap Traps for 4 seconds while they remain in the area." Yet in the recent games I've had I've seen people nearly instantly get trapped just as they moved out of the first trap. It's not like they can get permarooted at the same place, but I'm pretty sure it was less than 4 seconds, even if you deduce the 2 seconds of the root. (like, 0.5 seconds after leaving the first trap or something).

Anyone encountered the same problem?

Hesitated to post in report a bug, cause I'm not entirely sure and wanted to know if anyone had similar problem