Yes, hanging on to the wrong AP is a typical device problem - it is up to the client to scan in the background and make its own decisions.

Ubiquiti Unifi does have an option called minRSSI which allows you to set a minimum signal level of a client. If it goes under that value, the device will be disconnected from the network, essentially triggering a kick where hopefully the client will figure itself out. However, it is entirely possible that when this happens the client will just reconnect back to the AP that it was previously on. Sometimes WiFi drivers are stupid. The Unifi AP will not kick a device twice in the same session.

My laptop does this in Linux, always hanging on to my AP upstairs when I go down or vice versa. In Windows, it works perfectly and seamlessly.

In the future 802.11r and 802.11k will hopefully solve these issues once and for all one day.