With my winter gloves on, a couple of times when only trying to reset trip1 I have not felt the button move so pressed and held again, and both trip1 and trip2 reset to zero - seems like I hit the button again as trip1 was about to flash and reset the them both in quick succession. really annoying when you are using trip2 as a multi day trip total!
Tip: You can also reset the avg fuel consumption the same way.