Well, I wouldn't say normal, but it can happen and certainly not ideal. In fact, we don't recommend adding stabilizer to the skimmer at all. You should use the method listed below.
Adding CYA: To increase CYA via granular stabilizer, place the required amount as calculated by the Poolmath calculator into a white sock and place in the poolside skimmer basket. For those concerned about suction flow to the pump, suspending the sock near a return jet or from a floating device will also suffice. Best never to allow undissolved granules to rest directly against the pool surface. Squeeze the sock periodically to help it dissipate. Once dissolved, consider your CYA adjusted to that programmed (target) level. CYA test readings should show a rise in 24-48 hours, however some pools may experience a longer delay to fully register. Best to confirm final CYA in about 5-7 days before adding any more stabilizer/conditioner.
I personally have had issues with these filters. Nor can I verify, but I believe since the cartridge is really flimsy the pressure actually pushes the cartridge down exposing the center column and allowing particles to pass. If you were to put a little weight on the top of the cartridge you’ll see how easy it is to expose that center column.