Shouldn't be a problem since about 2015 (?), when exchanges were modified so that calls are cleared by the caller OR the called party hanging up.
That's what I thought but it certainly at the very least holds the line open on the base station presumably blocking incoming calls. I'd have to try calling the landline next time to see if it ACTUALLY holds the line open or not.
I think I figured out the problem though, the base stations are a bit crap so mum with her arthritic hands isn't putting the handset back straight so it doesn't hit the charging contacts thus doesn't hang up. That's pretty poor, every other DECT handset I've had guide the handset into the dock so you know 100% its docked fully.