I am using PP CC 2015.3 to match the setup at work.
When animating stills last night, I encountered a mystifying
"drift". The stills would continue to move a bit past the end point
set in the panel. I tried deleting the keyframes and resetting,
to no avail.
First guess would be they had curves on them and need to be reset to linear.
Dell Precision T7600 (x2)
Win 7 64-bit
Adobe CC 2017.1 (as of 8/2017)
256GB SSD system drive
4 internal media drives RAID 5
Typically cutting short form from UHD MP4, HD MP4, and HD P2 MXF.