Hi Jon,
Your code works fine when pasted in a blank document.
I don't get html parsing errors, although I cannot check your "uos_add_insert" page.
You may need to call <master src="blank-master"> and change rows to 6 or more to see the htmlarea. Try in a blank document by calling <master src="blank-master"><formtemplate id="new_uos"></formtemplate>
Did you check the allowedTag and allowedAttribute parameters in the kernel? Do you have code that is "older". Is htmlarea actually available (check blank-master). Is javascript not blocked? ....
BTW, {B I URL} buttons are from the richtext widget not from htmlarea.