Grappling Bugs

[Gadwin]

When I grapple with a heavy shield equipped i get this message and am paralyzed until the grapple ends:
"You must have a free hand and use a light weapon to attack while grappling."

The paralysis -AC debuff applies for the full duration of the grapple and you cannot attack regardless of if you take the heavy shield off, then.

When grappling with nothing in either hand, the -AC debuff does not apply, and you can attack as normal. Throwing a heavy shield on after the fact does not trigger that message that starting the grapple with a heavy shield would.

The character has no grappling feats and is a level 23 tiefling barbarian. I have no idea if this is an issue with all shield types or not.