Hi,
ExtJs changed their license to GPL which is not compatible so I could never upgrade it anymore and shipping the ExtJs scripts with mojoPortal added a lot to the file size so I dropped that skin and removed the ExtJs scripts from our package. However since the scripts already exist on your installation you should be able to continue using it. I would make sure your skin uses the new stylesheet combiner and contains the ScriptLoader as documented here:
http://www.mojoportal.com/important-skin-changes.aspx
Note that its possible that the ExtJs CSS is changing those elements. since it is loaded above the main css I think you could explicitly put that back by adding:
strong { font-weight:bold; }
em { font-style:italic; }
at the bottom of your main css file probably stylelayout.css
Hope it helps,
Joe