When typing an email in the Live email version included with Win 8.1 the font will suddenly decrease to the point where it is unreadable.

When typing an email in the Live Mail version included with my Win 8.1 program, the font will suddenly decrease to the point where it is unreadable. The problem has something to do with dragging my hand on the mousepad, but I can't duplicate the problem while watching. The font can be enlarged using the font control menu, but it still shows up as the minimized font when the email is received by the addressee. The only solution I've found is to delete the message and restart Live Mail. also, this is not a problem that is resolved by the Zoom control in the upper right corner. Help!!