Guided Access disabled after being removed from charger

I work with students who use their iPads as communication devices. We always provide the student's devices with Guided Access enabled. I have been making classroom visits to check on my students' progress. I have heard from many teachers that they are using their device as a camera and not for communication. This should be impossible within Guided Access enabled. When I went to check, low and behold Guided Access was not on and a ton of apps were attempted to be opened/used. The teacher's were unable to tell me why Guided Access was off. Through trial and error, I discovered these students' devices (while having Guided Access enabled and on) when plugged in would automatically turn off Guided Access when plugged into the charger. When they were removed from the charger, Guided Access still was disabled. Am I missing something? Or is there a glitch?