bug?

I just discovered that something I used to do doesn't work the same way anymore... I have one of those 24" monitor HDTV style monitors with a whole bunch of pixels. My eyes are still good so a 12point font is good enough for me but when somebody comes into my office and needs to look at code I have to make adjustments. What I have been doing is creating a new frame (C-x 5 2) and using the options menu cranking up the font size to 18pts. Then I can maximize the frame and people looking over my shoulder can see. It used to be that such a font size change operation was frame local. That behaviour has changed making the operation global. If I had to vote, it would be for the previous behaviour... Of course, it is possible that I have missed something that toggles all this (or maybe just suffering from a bit of wishful thinking).