WMS layer incorrectly calculating the bounding box

[tastle]

The problem can be seen here: http://openlayers.org/dev/examples/wms.html

Zoom out as far as possible, then move in one scale level. The difference is very noticeable. Below are the URLs generated for the world map at both levels for a quick comparison.

Incorrect bbox (note 270 max y):

 http://labs.metacarta.com/wms/vmap0?LAYERS=basic&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&EXCEPTIONS=application%2Fvnd.ogc.se_inimage&FORMAT=image%2Fjpeg&SRS=EPSG%3A4326&BBOX=-180,-90,180,270&WIDTH=256&HEIGHT=256

1 Level in, correct bbox:

 http://labs.metacarta.com/wms/vmap0?LAYERS=basic&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&EXCEPTIONS=application%2Fvnd.ogc.se_inimage&FORMAT=image%2Fjpeg&SRS=EPSG%3A4326&BBOX=-180,-90,0,90&WIDTH=256&HEIGHT=256

You'll see that the max y value is set to 270, and the server is returning some type of image based on the poor request.

This is a problem when overlaying data from other sources, such as a WMTS, where the image returned for a given tile won't theoretically shift with the rest of the data.

Any thoughts would be appreciated. I update this as I find out more details.