Microsoft has recently acknowledged the 5th issue in Windows 10 cumulative update KB4489899 for version 1809 (October 2018 Update).

KB4489899 was published included in the Patch Tuesday cycle on March 12 and originally included just two different known bugs.

According to the updated KB page, installing KB4489899 could break up the Preboot Execution Environment (PXE) on Windows 10. Microsoft explains the following:

"After installing this update, there might be issues while using Preboot Execution Environment (PXE) to start a tool from the Windows Deployment Services (WDS) server configured to make use of Variable Window Extension. This may cause the bond towards the WDS server to terminate prematurely while downloading the look. This problem has no effect on clients or devices that aren't using Variable Window Extension."

"A fix is on its way"

As the company says it's already working on a fix, which may be contained in a future release, Microsoft also recommended users to disable the Variable Window Extension on WDS server. There are many techniques to do this, and you can check them in full around the update KB article.

There aren't any specifics regarding when a fix could be published, but Microsoft is anticipated to release new cumulative updates for Windows 10 later this month. However, since no details were shared, I believe there are bigger chances with this bug to be resolved with the cumulative updates coming the next Patch Tuesday, that takes put on April 9.

The bug has also been confirmed in the other Windows 10 cumulative updates published this month, including in KB4489868 for Windows 10 version 1803 (April 2018 Update).

Obviously, this bug won't affect consumers, therefore if you're a home user, you should check the other known issues that happen to be acknowledged in this month's cumulative updates.