@tridge What is “large” in that case? Is it enough to connect a GCS during flight, causing an initial full parameter download?
I have had some trouble with very large MaxT values recently, causing major flight instability and also a crash with ArduCopter 3.5-rc4 (see ArduCopter-3.5-rc4: long loops).
Is there anything in the log that allows to identify this situation by lookin into the log?