UPDATE: Adobe commenters below point us to OSNews, which states:

The concerns in question have to do with charter and scope, and are not exclusive to Adobe. The problem seems to be that all these documents - Microdata, RDFa, Canvas 2D API, HTML5 document - are all lumped together, and some are confused about whether or not an objection to a single one can block all of them. The answer is clear: no, it cannot. In other words, Masinter's objection does not block HTML5.

They further claim that since the objection was discussed in a publicly accessible archive, it wasn't secret either. A tempest in a teapot, perhaps, but the debate concerning Flash and HTML5 shows no signs of breaking soon...

ORIGINAL: Daring Fireball has linked to a post by Ian Hixie that states, while Adobe has been publicly supportive of HTML5 -- sometimes seen as a open rival to their proprietary Flash technology -- they've secretly but a block on the publication of the specification.

Gruber expands as follows:

My understanding is that Adobe is trying to block the API spec for the canvas element. The canvas element hasn’t gotten as much attention as the video element, but clearly, 2D graphics in canvas is competitive with Flash, and it appears that Adobe’s plan is to sabotage it via W3C politics.

Would this be analogous to Microsoft trying to block JavaScript and CSS back during the height of ActiveX? (If you don't know what that is, thank the open, standards-based web).

Adobe was apparently supposed to have made the objection public 4 days ago but as far as we know have not followed through on that yet.

This may sound like a bunch of geeky web geek geekery, but it involves the next step forward in web technologies -- something which in the past has brought us the likes of Web 2.0's Google Maps and Facebook, WebKit (the basis of iPhone Safari) and Twitter, and now seeks to give us less resource intensive, vendor-independant specs for the future.

And since the iPhone doesn't (and the iPad won't) support Flash, HTML5 is how Apple hopes we'll be enjoying the dynamic web for a long while to come.