Grob Twin Astir getting "stuck" in a slip

I was flying my club's Twin Astir and noticed that if I put it into the deepest slip I can, by first pushing the rudder all the way to the floor and then compensating for yaw by using opposite bank, the plane doesn't come out of the slip very willingly. I have to actually put opposite rudder to get the desired timeliness of response.

On anything powered I've ever flown, as well as for my one flight in a 2-33, the planes snap out of the slip on their own. By removing rudder pressure, the plane reduces slip accordingly. I've certainly never had to *push* on the opposite rudder to resume normal flight.

Of course, those planes have super boxy and wide fuselages, whereas the Grob has a much finer shape. The Grob also has a smallish rudder and vertical stabilizer compared to, say, a Cessna.

Lastly, the Grob has a T-tail, which could lead to some weird airflow issues, but typically I associate T-tails with attitude control issues, not yaw.

Anyone seen this kind of behavior? If so, is this normal for all fine fuselages, or is this unique to the Twin Astir?

P.S. This doesn't happen in shallow slips, there seems to be a knee in the flight behavior.