LG G2's native camera app does not want to record anything

Here is my problem :

If I try to record a video using my LG G2's native camera app, the recording does not start and tells me that I cannot record a video while calling someone. However, I am not calling anybody! I tried to completely close any app that could call (native phone app, skype, ...) but it does not work... the message is still showing up...

Edit : I forgot to mention that this only happens in "Normal" mode, every other modes work fine.

Edit 2 : It used to work fine, but this problem just randomly popped up and I can't get rid if it...