To my understanding it seems you are doing things right (at least in those cases that came to mind when I read your problem).

A few other thigs came to mind:
-Do you ever modify the x/y/z or pan/tilt/roll directly in another part of your code? (outside of the c_move/c_rotate functions)
-Are you animating your model? If so, are you using the POLYGON flag for the entity? Try to see what happens withought POLYGON.

On a different aproach to your problem also consider the following:
-the problem might not be in your code, it might be in the model you are using.
-Open the model in med. Are the feet at the axsis origin? Or is the waist around the axsis origin?
-Open your model in med, Object menu -> Transform Global -> Center Model, then save the model and test it again in your script (make a backup copy of the model first).
-include "default.c" in your main script. Run the code and press "F11" two times. Repeat the process that is giving you problems while you observe how the collision box behaves.

Searching for other possible causes... The problem might not be in your script nor in the character model, mabe it is the object you are colliding with.
-Is the object you are colliding with a WED block or another model?
-If it is a model... Is the origin at the center of the model? (you can check this in MED)
-Try to use c_setminmax(object); for the object you are colliding with.
-include default.c in your main script, run the game and press F11 twice, but this time look at the collision box of the object you are colliding with.