Just tried this on my iPhone 4 (yes 4!, iOS 7.?) and I get 4 when adding 1+2+3 quickly, and sometimes 10 or 11(!?).

Looks like this is a feature, not a bug, or else it would have been fixed sometime in the last 8 years! /s

Is 4 your daily? I miss my 4S and I'd replace current 6S with it but if I could bring performances. Beautiful phone.

I have a newer iPhone through work, so my 4 is only used for calls, sms and music. I'm keeping it until it dies and then moving away from Apple. What I really want is a true GNU/Linux phone.

Another datapoint: iPhone 4, iOS 9.3.5 does not exhibit the bug.