Testsigning breaks Windows Update?

I had fresh Windows 2012R2 SUT with test signing mode enabled, and when I tried to run Windows Update it failed in strange ways. Then I disabled test signing, and it seemed to be installing updates. Is it a known caveat?

The only thing I know for sure is that Windows Update can find numerous ways to break itself, with or without our help.

We have spent – quite literally – months of time dealing with Windows Update issues on systems with a product we’re developing. We found that problems were often random, unrepeatable, and without any readily identifiable cause.

I’m sure that’s not the answer you wanted from this thread, but I’ve been both shocked and bewildered at how very broken Windows Update is, and just in case you didn’t know this…

Peter
OSR
@OSRDrivers