ActiveX control textbox font keeps changing

Hello...I'm using v2010 and am using an ActiveX textbox with the following properties: AutoSize=False, EnterKeyBehav=True, MultiLine=True, ScrollVertical=True.
Initially, everything with this box was fine. However, I now find that when I click inside the box, then click outside the box, the font of the text inside the keeps getting smaller. The dimensions of the box don't change and I don't want it to. But I did initially set the font to, say, Verdana 12pt. This fontsize should not change. I can't find a property that would control this; I have made sure that AutoSize=False, as above.
I have read blogs that said this is a known issue with ActiveX controls and I should switch to Form Controls. However, the textbox feature is not available and I'd rather not have to use sophisticated VBA coding (as a Change Event or something) to "reset" the font size to what I want anytime anyone edits the textbox. How do I keep the textbox font from changing?
Your help is most appreciated.
Thank you very much.
- Al