Is this happening on a Single book?
Auto-repair of code does not always put the fix for a missing closing tag, in the correct spot. A visual code inspection of where a Valid Bold was supposed to end, will probably be where the missing closing tag was supposed to be (Add there and remove at the end. These are
fun 
to find and fix)
Have you validated the CSS? RMSDK was known for ignoring the CSS if it had errors (it was only
supposed to skip the bad part
)