As to what might be the reason behind the pulling of the update is anyone’s guess since HTC has yet to make a formal statement on the matter. However there have been some reports which claim that some users were experiencing some issues with their handsets following the update, such as battery problems, which might be a possible reason why HTC has pulled the update.
It isn’t uncommon to see companies pull updates halfway rolling out, especially if the issues that follow the updates are too serious or annoying to ignore with a later patch. Of course those who downloaded the update will have to roll their OS firmware back if they don’t think they can live with the issues, but for now if you have yet to receive the update, we guess you’ll have no choice but to wait until a more stable version has been released to the public, which hopefully won’t take too long to arrive.