I just use the oem kawasaki filter on mine.. never had any issues. I have used k&n before without issues though on my k9 gsxr 600. Probably people over torque using the nut I suppose could cause an issue. I just put them on hand tight and never reuse them.
K&N is the main reason Moto America, AFM and likely other clubs completely disallow aftermarket oil filters. I was personally in a race where the dude in front of me had his K&N filter comp apart and dump oil on the race line. Luckily, I didn't get caught up in the mess but it could have been ugly. I run OEM and never worry about a thing.