At least their software QA went haywire... 2.11 was released with the sole purpose of resolving the issue which arose in 2.10. So 2.10 should never have been released in the first place.
A word of advice to anyone who downgraded to 2.09 in order to resolve the issue: If Software Update (10.6 and 10.7) or the Mac App Store (10.8) advertises both versions of the HP Printer Software (i.e. version 2.10 AND version 2.11), please apply the update to version 2.10 FIRST; then update to 2.11. That way, you won't run the risk of your system's updater wanting you to downgrade to 2.10 after having applied 2.11.
That is what happened to me. My system (10.8, so it's the App Store) advertised availability of version 2.10 AFTER I applied 2.11. In the end it didn't matter, because no downgrade actually took place, but it certainly was a bit of a strange issue... Apparently, Printer Driver Updates aren't cumulative, or at least not in the 'eyes' of Software Update/the App Store...
Anyhow, I'm really glad this blatent bug has finally been resolved.
And just to stick with the promise I made in the previous post: I have no problems whatsoever when printing using software version 2.11. So there's no need to wait any longer.