Interesting. Please list all zones that you encounter with this issue. If you have to pass a zone line to get to a zone with an issue could you please type the following before you zone in:
/show_map_style_name 1
When you zone it will print the following into your chat window:
Map style name: <name>
Please post the <name>.
Type
/show_map_style_name 0
to get rid of the chat window spam again.