A pair of reproducible buglets in 2.1.20 Pro on Mac:
If you have an end repeat barline immediately before a meter change, then cutting the meter change incorrectly cuts the barline too. (Actually, deleting the meter change has the same effect, but Dorico then immediately corrects for it by re-adding the barline, almost – but not quite! – too fast to see.)
Pasting a meter change immediately after an end repeat barline incorrectly overwrites the barline. (Again, adding a meter change using the popover has the same effect, but again Dorico immediately corrects for it.)
It looks to me like someone found a bug when meter changes are deleted and added, and fixed it with a hack (by forcing Dorico to re-add the barline as soon as it’s been deleted), but forgot to apply the same hack to cutting and pasting.
Yes, they certainly are; when you select one, others get highlighted too. No doubt this is the cause of the problem, but it can’t be intended behaviour.
AFAIK, special types of barlines are really meter changes, with the meter hidden. If you open the properties panel (Ctrl-8), select the barline, and deselect the “hide time signature” property, the time signature appears in the score.
However, it seems you can’t edit the time signature value directly in the properties panel - you have to create the time signature and then create the barline.