Parts display and editing

Using Musescore 3 on linux mint.
File "La_Marseillaise_French_National_Anthem trio.mscz"
I load the downloaded score, with 3 parts (all violin "La Marseillaise" but this happens with others). It loads with the file name in the top tab, then four tabs below, L to R: the complete piece, then the 3 parts, but with slightly different names that they have in the score (in the score they are all Violin, in the parts tabs they are Violin, Violin-1 and Violin-2, but all with an accent over the 2nd i in Violin. This is puzzling but not really important. I choose the 3rd part (Violin III in the header), and change the instrument to Viola. This works very well. If I change it in the left tab (showing 3 staves), it changes, but the fourth tab stays unchanged. so I now have it as both the original Violin, and as Viola. If I go to the 4th tab where that part is displayed on its own, and change it there, then it does not change in toe 1st tab, where the 3 parts are displayed together. Although the displays of the 3rd violin were initially the same, they are now different, and seem unconnected.
Russell