Any update @zoran? This is still a problem. To be more precise, the unwanted definition automatically gets added when there are more than one popular meanings already present.
Can you please raise the issue again with your developer? I have been having this problem for months every time I try to add a tag by pressing the down arrow followed by the enter key. Strangely enough, if i use the mouse to select the tag from the dropdown menu, it’s fine (but it’s more time consuming when you tag a lot of words).