Hi there, thank you for the post. I just wanted to add a few observations on behalf of the Internet Explorer team.
Firstly, no browser offers a perfect implementation of the Canvas 2D API specification to date - we've documented and shared a few examples from our test suites here: http://samples.msdn.microsoft.com/ietestcenter/#html5Canvas
As has been well noted, the IE9 build tested was our beta.
Secondly, in response to the specific issues raised, Giorgio Sardo has posted a response on his blog here:
We'll update this entry over time.
Thanks for listening,
Tim Sneath | Microsoft Corp.