Of couse I did. It also happens with new web files and new projects. The upper pane of split web pages is always magnified and does not respond to the Zoom Out command. Deleting the prefs does not help.
The trouble is that there is zero difference between panes. They are identical, using exactly the same code, so there is no reason why one would work but not the other. However, I am wondering if the zoom is set to such a high number that zooming out just appears to do nothing, because the zoom is beyond anything zoom can handle (uh, if you see what I mean). Have you tried hitting Zoom Out again and again and again and again to see if this is the issue?
On the other hand... Which web page are you looking at? Zoom In and Zoom Out for web pages does nothing more than enlarge or reduce the text, so it would do nothing for a web page without text.
What system are you using?