That's a known issue with those piece of **** Costar stabilizers.
Funny thing, there are TWO kinds of wires that come with these stabilizers. If the wire is completely FLAT on the table, you will not have issues with ORIGINAL CHERRY KEYCAPS ... but if you stab wire has his little "bent part" standing up from the table, you will get this god forsaken rubbing.
Newer revisions of I:C keyboards come with the "flat" Costar wire, Switchtop is also selling those with flat wires.
The only other solution is to carve out a thin layer on the inside of the keycap - as you did.