Flip Case magnet tab failing after pressing

[Johnellisimages]

Has anyone had issues with phone universal flip case closing tabs (magnet) not working after pressing? Didn't think it would be an issue but after pressing 4 and letting them cool, I went to bag them up and found the tab wouldn't stay in place, seemed to have lost its magnetic stick. I called the supplier who said cover it with old mouse pad or something, i happened to have thin silicone sheet which I cut a couple of small pieces off and covered the tab, seems to have worked. Just sharing in case someone else has the same issue, maybe it's common knowledge, not a problem I anticipated.

[ICF]

I believe the heat reduces the magnetism so you either need to have the tab outside of the heat press (if possible) or have something cover the magnet whilst in the press.