ID 216362 - Large Sequences(500+ panels) slow to step through in Pitch mode

Problem summary
Sequences of 500 panels or more are slow to step through in pitch mode in some situations
If you load Sequence A (500 panels ) then step back to the project browser, load sequence B (500 panels)  and enter Pitch mode, use the arrow keys to step through the sequence,  the sequence becomes will become laggy, and stutter some panels are completely skipped by during the lag depending on the speed you tap the arrows. 

Customer reported version

5.2v5

Steps to reproduce

1) load Sequence A (500 panels ) then step back to the project browser

2 )load sequence B (500 panels)  

3) enter Pitch mode

4) In Pitch Mode: use the arrow keys to step through the sequence,  the sequence becomes laggy and stutters, some panels are completely skipped over during the lag depending on the speed the arrows are pressed.

Reproduced by support
Flix 5.2v5 - os x
Flix 5.2v3 - os x 

Unable to reproduce the bug in:
5.1v6 - os x 

Earliest version tested
5.1v6 - os x 

Expected behavior
Pitch mode to be responsive when arrow keys are used for navigation in large sequences

Actual behavior
Pitch mode is laggy when multiple sequences have loaded and arrow keys are used for navigation