Some attribute vals being passed into mw.html.element() are numbers instead of strings, and mw.html.element() isn't set up to convert things to strings automatically.

As a workaround, should work fine to force all the vals to strings.

(In reply to comment #1)

Some attribute vals being passed into mw.html.element() are numbers instead of
strings, and mw.html.element() isn't set up to convert things to strings
automatically.

I've hit this a few times as well, although so far I hit' it before committing, it sure is annoying.
Fixed in trunk, mw.html.element converts booleans and numbers to strings.

See bug 30774. Let's backport r96307.

Hey this is valid, it just depends on 30774. :)

r96307 & r96310 fix this when backported.

Merged to 1.18 in r104753, 1.18wmf1 in r104754 and pushed to site