[Typo3] Problem encountered on upgrade frpm 3.7.1 to 3.8

[Chris Watt]

I have updated a Typo site from 3.7.1 to 3.8. Everything nearly working OK 
after some intial problems. The only problem I can't solve now is that all 
the text that uses Headings via RTE is now displaying as <h4 class="">the 
text that should be heading 4 font</h4>  instead of using the h4 style. My 
css has not changed. No matter waht I try I can't get it to display in the 
heading font styles as it did in 3.7.1.
Anyone got any ideas of where to look?

Thanks.