When not using a DOCTYPE, browsers work in quirks mode, which means that some CSS styles are not applied the way web standards command. I suppose you observe the problem in Internet Explorer. In IE6 min-height is not supported at all, while in IE7 min-height is supported only in standards mode (with DOCTYPE).
The workaround is to supply IE (only IE) with a height style, instead of min-height. In quirks mode this will work as min-height. To do this, you should use one of the famous CSS hacks for IE 6:
* html .something
height: 200px ;
_height: 200px ;
These two hacks work in IE7 in quirks mode, so they should do the job.
the Telerik team