After a few copy-paste of slurs from one measure, suddenly a new slur is created from the beginning to the end of the score
2.1 version / Windows7
1) « Untitled » score
2) First measure : enter two half notes with a slur
3) Create parts → new all → Ok
4) Main score: Copy the first measure
5) Paste in Part first measure
6) From part now, copy first measure
7) Paste in main score first measure
And so on (from step#4), 6 times
Without particular reason, the seventh time, after you copy and toggle in the main score for pasting, you observe that another slur appears and extends from the beginning to the end of the score (image below)
At first glance, it seems harmless since after Save/Close/Reload, this slur is not shown. But after repeat 3 times, now (instead of 6) the same steps again the slur reappears.
And of course, the score size is growing and leads to bad things...
For this reason, I choose "major" for status (ie between harmless apparently and potentially dangerous, in any case, unexpected)