Most probably the reason is the change in inharmonicity after the pitch raise. As a rule of thumb:
For a 20 cents raise, you get a decrease of 2% in inharmonicity.
For a 50 cents raise, you get a decrease or 6% in inharmonicity.
For a 100 cents raise, you get a decrease of 11% in inharmonicity.
For a 200 cents raise, you get a decrease of 21% in inharmonicity.
If the inharmonicity changed and pianoscope is still using the pre-raise values, the needle moves more erratic while the higher partials decay in the sound because it expects them to be at other relative frequencies.
So I recommend to remeasure the inharmonicity after a pitch raise larger than 10-20 cents which should fix your problem.
