Failures from XSLT in FF3.6a1 with "body onload"

I have an extension (wmlbrowser.mozdev.org) which uses
nsIXSLTProcessor in an XPCOM component to transform WML content to
HTML.

In Firefox 3.6a1, the transformation fails with

[Exception... "Component returned failure code: 0x8000ffff
(NS_ERROR_UNEXPECTED) [nsIXSLTProcessor.transformToDocument]"
nsresult: "0x8000ffff (NS_ERROR_UNEXPECTED)"  ... ]

The error seems to be caused by "onload" on "body" in the XSL - if I
take the onload attribute away then the transform succeeds.

But if I save the WML and XSL to disk, and add in the appropriate xsl-
stylesheet PI, the transformation succeeds.

Is this a known issue, or something I should raise a bug on? The
nearest bugzillas seem to be

https://bugzilla.mozilla.org/show_bug.cgi?id=386856
https://bugzilla.mozilla.org/show_bug.cgi?id=493585

but neither seems an exact match.

Matthew