When you type a positive value into one of the sample-offset fields of a track in the MIDI Offsets Window and hit return, the value will replace whatever value was there previously (this is how all other modifiable fields in Pro Tools work). However, if you type a negative value (e.g. "-10") into one sample-offset fields and hit return, the negative value will be subtracted from the previous value. This is inconsistent with the way all other modifiable fields in Pro Tools operate.This issue has been fixed in Pro Tools 5.3.1.