I have the same problem with burst mode. It should be something to be turned on or off not linked to flash or the button press. Besides this happens when the phone is mounted on a tripod and whether you use the side button or the dot on the screen. In timer mode I certainly don't hold anything down because i'm usually try to get into the shot with friends.
As a side note does anyone else feel that the screen on off button being opposite of the side volume button is a problem? I can't count how many times I have accidentally turned the phone screen off with my thumb while trying to use my index finger to take the shot...sometimes losing the shot I wanted. Bad ergonomics imao.