Lol, i've had the same experience... I never check the mode of fire, so much easier in life, haha.
had that with the STG44 yesterday!
*picks up STG44 at main base Falaise
*comes in front of 5 canucks
*DAI
*fires one bullet FFFFUUUUU
*gets sten gunned brengunned and even PIATED by canucks
Or when i forget to click auto back with the brengun
FFFUUFUFUFUFUFUFUF