It shreds into tiny long bits of spaghetti paint peelings, clogs up the sandpaper on the 2nd/3rd pass. Normally you can just lightly sand a bit of woodwork to provide a key without too much trouble but not with 4yo waterbased gloss. It's a bloody nightmare to get a nice flat surface with tiny peelings everywhere. Waaay more effort than it need be... Aibu?
I've got another 'keen'... Ouch!