Microsoft cleared up an annoying issue that vexed some of its Windows Vista users. When those unfortunates attempted to install a prerequisite, the Servicing Stack Update, their machines began the reboot cycle noted previously.

At the Microsoft Update Product Team blog, the group enlightened everyone with an assessment of why this looping behavior took place:

So what caused the problem? Well, the SSU has special code to check whether there are any pending reboots or other updates to install. If it sees either of these circumstances, it prevents the install from starting. During our investigation, we discovered that there were a few unknown and rare events during the middle of the installation of the update that could cause the update to think it needed a reboot to complete the installation.

An update for the SSU will stop this annoying little behavior from happening for Vista customers, to allow them to proceed with the Vista SP1 installation via Windows Update. Vista users who opt for the standalone download of Vista SP1 will avoid the whole SSU prerequisite check entirely.

The disclosure comes as Microsoft moved to try and bring an end to the availability of the XP operating system as an option for PC buyers. Vista’s heftier than disclosed hardware requirements and assorted driver issues that affected even highly placed Microsoft executives compelled people to choose XP.

That doesn’t help Microsoft’s profitability, but at the same time the company’s own internal admissions of problems with Vista didn’t help anyone, including themselves. If Vista is a couple of service packs away from being a stable, viable OS, Microsoft should not stop XP sales until then.

SP1 has been released to manufacturing, anyway, meaning it’ll wind up on brand new computers in the not-too-distant future.  But unfortunately for people with "used" computers, SP1′s availability is a little ways off, as well.

"In mid-March, we will release Windows Vista SP1 to Windows Update (in English, French, Spanish, German and Japanese) and to the download center on microsoft.com," writes Microsoft’s own Mike Nash.  He later continues, "In mid-April, we will begin delivering Windows Vista SP1 to Windows Vista customers who have chosen to have updates downloaded automatically."

Microsoft is claiming that this process will ensure a smoother rollout, and there’s no reason to believe the company’s wrong.  Microsoft may have effectively halted sales of Vista until mid-March, however, as people hold out for the latest thing.  And current owners have gained nothing by learning of SP1′s impending release.

Meh.  In any event, we’ve got to give Microsoft a nod for catching us by surprise once again.  Let’s hope the surprises continue with SP1 actually making significant improvements to Vista.