It appears that is impossible to move a bar from a screen to another.

Reproducible: Always

Steps to Reproduce:
1. Create a vertical bar
2. Put some plasmoids in there
3. Plug another screen so that the new screen is on the opposite side of the vertical bar
4. Show the options of the bar and try to change screen edge
5. Drag the bar to the edge of the 2nd screen, so that it has to cross in between the 2 screens.
6. Now the bar is gone.
7. killall -9 plasmashell
8. plasmashell &
9. Now the bar is again in the original place, but it's not as wide as before

Actual Results:  
The bar is gone

Expected Results:  
The bar goes to the other screen