If it were happening to me I'd view the html source code in IE and look for clues.
I have also found that this happened in CF9 as well according to this post: http://forums.adobe.com/message/3159524#3159524
Message was edited by: planomax
For future users, here's what fixed the issue:
I downloaded a newer version of C\ColdFusion10\cfusion\wwwroot\CFIDE\scripts\ajax\resources\ext\css\ext-all.css and it appears to be OK.
The version I used is 3.4.
Hopefully nothing else has broken by doing so.
I tried to replace the ext-all.css 3.4 version into the path you mentioned. However, it is still showing the reduced popup calendar. Any hint to fix it?
I'd caution everyone on replacing the EXT or YUI libraries that are delivered with ColdFusion, as the UI tags are wrappers that are tied closely with a particular (and out-of-date) release of those libraries. This is one of the main reasons that many experienced devs are recommending people not use the CF UI tags at all and instead write their UI stuff directly in HTML/CSS/JS with your UI library of choice (jQuery UI, ExtJS, Bootstrap, Zurb, etc.).