I reckon most everyone using SPDs or any other clipless foot retention has fallen over at traffic lights or in similar awkward situations at least once whilst getting used to it.
For me it was just a case of sticking with it and you get used to it (much like riding fixed TBH).
I have occasionally popped out when applying a lot of back pressure on the leading foot, i.e. skidding, but generally no. It's not exactly a disaster if you pop out, just sit down, use your brake if you need to and clip back in: simples :)
I reckon most everyone using SPDs or any other clipless foot retention has fallen over at traffic lights or in similar awkward situations at least once whilst getting used to it.
For me it was just a case of sticking with it and you get used to it (much like riding fixed TBH).