2nd curtain and HSS cant co-exist by virtue of the way they work so its not an error or ommision
... but I'd like an option to switch between hss and 2nd curtain sync, with the current system it auto-switches to 1st curtain sync if <x-sync. If you enable the mutually exclusive 2nd curtain it cannot auto-switch to hss.
1st curtain fires an intantaneous burst at the start of the exposure say 1/10000 sec long
the remaining duration exposes ambient
Guess again :-) ... a full-power flash on Canon flashes like the 580ex is *1/800* long - I was also surprised how slow flash is when I read that, though at normal power outputs it gets faster.
with pulsing you might be thinking of multi mode and stroboscopic flash where the flash fires multiple reduced output bursts at a programmed (by you) frequency for the duration of a long exposure
And with "pulsing" I meant the hss system (continuous light) which is implemented as a successive series of low-power flash pulses. Sorry it was confusing, I couldn't come up with a better word do differentiate what hss does vs. "Multi-Mode"/strobe flashes.