The usage of "sir" for female military superiors in Trek (and BSG) is grating, arguably misogynistic and (as far as I know) possibly Ron Moore's idea as it turned up in TNG once or twice.
Apparently, though, senior naval officers have traditionally referred to juniors using "mister" regardless of gender, so the cringeworthy use of "Mister Saavik" in whichever movie Saavik first appeared in might not be incorrect.
The use of "Mister" to Saavik was completely correct and thus far from cringeworthy. The purpose is to be the exact opposite of misogynic because to refer to all officers with the same term is a psycological reinforcement of equality.
I must have completely misremembered that Voyager bit if the transcript above is correct.