Erratic MIDI Behavior Needs to STOP!

[Cayce]

Working on a complex session where the MIDI piano composition was causing CPU overloads, I finally had to create a new session with only that single MIDI piano track so that I could get the work done, then migrate my work back into the main session. Even in that isolated session, though, PT is incapable of allowing me to build this MIDI piano track without trashing my workflow.

In trying to patch in a 2-measure section, one attempt plays the piano sustains as they're supposed be, on both the pre-roll and the recording. On the next attempt, all pedal sustains are gone and notes aren't following the tempo.

With no other tracks or plugins to interfere with resources to manage this single MIDI track, what could causing this (other than the common knowledge of PT being garbage)?

Thanks.