Overstrike mode is the default edit mode for MusiCAD. This in contrast to the - still available - insert mode in prior versions.
Note-deletions will result in a rest of the same duration. A 1/4 note will overstrike 4 consecutive 1/16 notes etc.
On overwrite MusiCAD will take into account duration and position within a bar.
If default note-duration was selected as 1/8, <Enter> will overstrike the existing 1/2-note with result shown below.
Once more <Enter> when duration was selected as 1/1 results in::
Some trouble causing features are disabled during overstrike: