Default [Q] Strange behavior 3g/4G switch?

Hi,
When data is downloading on the phone on 4G, then when a quit an 4G area, the phone keep trying downloading in 4G, not switching back in 3G.
Causing no network i can't be reachable, only way is rebooting my phone.
Did somebody already seen this beahavior?
-Nexus 7-
-Galaxy note 3 N9005-