LS: left-side
RS: right-side
Created a task to mirror folderA on LS-PC to folderB on RS-PC
Ran task. Now both sides are the same.
Edited the task for 2-way sync:

Ran Attended Mode. Nothing to be done. OK, that is expected.
Added text.txt file to RS-PC and ran attended mode. text.txt was copied to LS-PC. Again, OK
Deleted text.txt from LS-PC.
Ran Attended Mode. Nothing to be done. NOK, that is unexpected.
text.txt was not deleted on RS-PC. Why? Seems I'm overlooking something basic here.