If I google for "Extjs rtl", I find that it is a bug in ExtJs. I also find there is a fix you can make.
Its a workaround for now until they fix it in ExtJs.
What I would do is copy the /ClientScript/ext-2.0 folder and name the copy ext-2.0rtl
Then make the edit in /ClientScript/ext-2.0rtl/resources/css/ext-all.css as indicated in the above link.
Then configure your installation to use this modified version by Web.config
<add key="ExtJsBasePath" value="~/ClientScript/ext-2.0rtl/" />
Hope it helps,