Well, I suspect that is kind of different but:
a) if you press and release the momentary crouch button while frozen, you do not crouch (even temporarily) when you are unfrozen (or during the freeze, obviously).
b) if you press and hold momentary crouch until you are unfrozen, as soon as you are unfrozen you will move into the crouched position but when you release the crouch button you stand up.
The above seems a logical and natural way for things to happen but the crouch toggle waiting for you to become unfrozen and then crouching the player may seem OK from a certain POV (ie you can store up your crouch to automatically duck when the freeze is removed) but illogical from another POV (ie you are not supposed to be able to do anything except press [use] when totally frozen).
In my particular case, it kind of ruins an effect at the start of a level. I have the player start in a small hole to bring his eye line down near to the floor, simulating him waking up from unconsciousness - which is how the previous level finished. The player is frozen whilst the view fades in and out from black a couple of times and then the floor of the hole is raised to simulate the player getting up from the ground. It works pretty well.

However, if the player presses crouch-toggle before he is unfrozen, he seems to rise up to the standing position and them immediately duck back down to his unconscious position when the freeze is released. This looks weird.
For a bit of additional information, if you are frozen and press crouch-toggle twice (which in a non frozen state would crouch you and then uncrouch you) the second press does not seem to take effect and you will duck when you are unfrozen but not then unduck (new word?). Perhaps this is because uncrouching requires you to to actually be crouched before it will take effect and this never happens in the frozen condition?