Windows Defender updates

Having this strange issue with updates for Windows Defender offered via Windows Update for last few days. Here's one example from the Windows Reliability Monitor:

Notice that WD update 1257.0 was successfully installed via Windows Update at 4:10 PM, but then it tried to install the earlier update 1248.0 at 5:53 PM on the same day, and that one failed.

I can understand that 1248.0 would fail because the newer 1257.0 update was already installed. The question is why/how is WU installing the newest version first and then attempting to install a prior, older one afterwards, especially when both updates were offered on the same day? 

PC is on and connected to the internet all day, though it may be sleeping at various times. And as far as I can tell, there's no effect on either antiviral protection or on overall PC performance so I'm just trying to understand what's going on here...

Anybody else seeing this?