It's a design flaw. If you get replacement headlights from the dealer, those new headlights will eventually do the same.

So your choice comes down to around $5 and 30 minutes or so of your time (remove front bumper and headlights if you have to) compared to weeks of waiting for your dealer to:1) tell you to just glue it, 2) argue with you before agreeing to glue it for you, 3) argue with you even more before finally agreeing to order new headlights... which takes a week to arrive.