The first shot shows the lowest note about to receive a grace note.
The second shot shows where the slash actually went, that is, the full-size note to the right of where the grace should go disappeared, and the expected new grace note showed up in the next bar. Never seen this one before.
Here’s a better shot of the second picture.
If you have a note selected and you hit the / key, it will be converted to a grace note (and if you select the grace note and hit / it will be converted back to a normal note again).
If you want to input a grace note rather than convert an existing note to a grace note, show the caret before you hit /.
As the picture shows, I entered the main note first. That is the lowest note in this case. Then I went back to add a grace note to it. Is that right? I think I have done this many times.
It looks like the caret wasn’t visible. Once you’ve selected the note where you want to add the grace note, hit Return or Shift+N to show the caret.
I see. Yes it worked this time. Thank you. I did it many times right by accident it seems.
… or rather by good intuition 