"ringing" high notes

I'm using  Pianoteq Stage. I've found that once I get into the keyboard range above C6, notes continue to sustain even though I have released the key. For example, using the Steinway B Prelude preset, notes do not dampen but instead decay very slowly when I release the key at F6 and above. I've noticed this with several other Pianoteq pianos as well. Has anyone else encountered this? I'm using a Casio Px5 as my midi controller. Not the best board, but I don't think this is the source of the problem.

I recorded it here:  https://drive.google.com/open?id=1sNE3e...IT4-6IYUrW