Pianoteq 3.5 & Cubase 5.1 - issue saving instrument setting

I just installed my update from Pianoteq 3.0 to 3.5 and I find that when using it with Cubase 5.1, I have an issue with Pianoteq saving the instrument setting.

If I have selected an instrument (other than the first one, C3 Solo Recording), saved my Cubase project and then re-open the Cubase project, I find that Pianoteq is set back to C3 Solo Recording.  The combination of Pianoteq 3.5 and Cubase 5.1 is not remembering the Pianoteq instrument when a project is re-opened.  In addition, in Cubase 5.1, if I attempt to change the preset with Cubase's preset selector, then I receive this error message: "Pianoteq v3.5.0/20091028, Internal Error occurred in param_interpolators. cc:206".   When responding 'OK' to this error message, Cubase 5.1 quits completely.  There is no trouble when changing instruments via Pianoteq's built-in preset manager. But no matter what, the instrument is not held constant between closing and reopening the Cubase project.

I still have Cubase SX3 installed and so I tried Pianoteq 3.5 with this older version of Cubase.  In this case, there were no issues saving the settings when opening and closing Cubase projects and there was no problem using Cubase's preset selector.   

Am I alone in observing this phenomenon?

(Computer= quad core PC running WinXP/Pro/SP3)