attr() not working in some cases in IE9

[hhelwich]

When i use attr() on an observe in an EJS template it seems not to work in an HTML attribute in IE9.
Other browsers (FF, Chrome, Opera) are working.
When reading the model attribute direct and without attr() it works in IE9 but of course it does not bind to model changes. Can you help?

I created a small example:
http://jsfiddle.net/hhelwich/XyAa9/

[daffl]

Thanks for reporting. Fixed via #498 and will land in the next release.