I've seen the report.
But I can't do much about it, as I do not have an M1, and by all likelihood it is bound to that.
What I do here, is
1) Check, if it really is not SynEdit.
2) Potentially help finding the location in the code, where something goes wrong.
1)
I ensured that even with Trev's editoroptions, it does not happen on my PC.
Also the log looks correct. It does not show any indication that extra commands are sent to the Editor (I.e focus moves, that may have side effects). The caret is changed while handling the #9 key. So even if any other unwanted calls to SynEdit happen, the caret has gone wrong while handling #9.
2)
I will provide details which code is involved.
Then if someone with an M1 and moderate debugging experience and willingness can step through that, maybe we can find the line of code that changes the value for caret-Y. (This may require several iterations of debugging, feedback, debugging something else).
It can then be checked, if the error is in the Pascal source (and hence in SynEdit), or if it is wrongly compiled.
In either case narrowing it down, will help fixing the issue.
If the process renders any information on the cause of the issue, then that should be added to the bug report. (Adding the whole process will clutter the report / I.e. if it goes to fpc, they will "love" reading about SynEdit)