Question for HP45 owners re. scientific mode

[dos]

I've wanted a calculator from the first series for a while, I took a gamble on this "untested" 45 on ebay for 40 bucks the other day (it came with no battery or charger):



It's in great shape and seems to work nearly perfectly but sometimes it won't switch to scientific mode, or only will if I enter the entire key combination (shift, sci, #) very rapidly. The unshifted fix button always works, and all other shifted functions are perfectly normal. Just wondering if this is a quirk of these models or if there's something weird going on.