I have tried your code and it works fine for me. I've tried many different things to try and create your problem, but it just seems to do as expected. The only thing I can think of is that you have an On Error Resume and you have run out of form to allow the new control size to fit. Normally you will get an error when this happens, but it wont be displayed if you have On Error Resume Next above the code.
thanks for the assist, but resume wasn't/isn't the problem. I tried a dummy control group with the same result as my problem. However, within the control group I changed the attributes of the checkboxes and labels ie visible/enabled/top/left etc and then changed the height and placement of the frame and voila! magic everything was 'right'. The internal checkbaxes had previously moved etc but the frame stayed elongated. Now eveything appears alright, so, make any changes to the frame last.