I was in trouble with similar behavior for weeks.
Actually using osmc 2018-12-1 with nebula skin, raspberry pi 3B, official 7" touch screen.
I figured out today that mainly, mouse cursor and touch interaction are independant but …
Default location of mouse cursor (top left) interact with the top “option bar” with a sort of roll over behavior. When i touch the screen this mouse cursor interfere with the expected action.
If i simply move one time that mouse cursor elsewhere with a mouse or rii remote, the touchscreen is working perfectly.
As i want to use alternatively touch feature and rii remote as mouse, i will look for changing the default position of mouse cursor.
I hope this can help some users.