When renaming a file from the Convert Tags -> Filename option, %track% shows a combined value of both the track number and track count instead of just the track number. The Track field in main window will show 10/37 but the "Tag - Filename" dialog shows 1037 instead. I've attached a screenshot of the Tag - Filename dialog as an example.
I found a workaround for this by using the $num function as so: $num(%track%, 2)
This will show the track number correctly.