I have noticed that the debugger pointer (green arrow in the left margin of the debugger window) and the 'current line' highlighter (blue line highlight) will sometimes get out of sync for one step. Other times the two items are still in sync, but they go to a blank line in the script (i.e. not a valid script step). It seems to always happen after the 'Pause Script' script step. (That may not be the only step that it happens after, but it always does happen after that step.)
The two items re-sync once you step to the next step.
See attached screen shots.