I've had problems like that, my solution for that was to wrap the dynamic content generated by WYSIWYG editors, into a div with a unique class, where to that class I've created a reset style sheet with standard attributes!
Ex.:
div.wrap_to_prevent {style, style,
style}
div.wrap_to_prevent input,
div.wrap_to_prevent textarea,
div.wrap_to_prevent h1 {style, style,
style}
.
.
etc
Basically, I've used a reset style sheet, but preceded all css style's with the class of my div, that way, it just affects the code inside that div, thus creating a brand new set of rules for that content.
Since 90% of my projects use WYSIWYG editors, with this solution I was able to work around that same problem...
Can't tell if this works for you, but give it a try!!