A simple fix is after you have posted the web page -
1. Open the workflow up on the workflow server under %programfiles%\Symantec\Workflow\WorkflowDeploy\Release\(Project folder name)
2. Look for Form.aspx
3. Now edit the Form.aspx looking for the tag <!DOCTYPE HTML >.
Remove this and your formating should go back to how you set it.
Hope it helps and the tech article that it relates back to in 7.5 is http://www.symantec.com/docs/TECH218478. We use 7.6 and this is what I had to do to correct the same problem.