Non current vehicles drop out of orbit

[purpleivan]

I've encounted this issue twice this afternoon, first time being after the fact, when I noticed that a vehicle in orbit of the Mun had changed from a 46km orbit to a near vertical descent towards the surface. The second time it happened I actually witnessed it myself, as I had the map view open at the time.

I'd switched to map view as I was climbing to orbit, just a few seconds before this image was grabbed. For a couple seconds the other vehicle (grey arc) was a nice 76km high orbit above Kerbin, when suddenly it changed to the suborbital trajectory in the image below.

The thing just popped from orbital, to very much suborbital as I was looking at it.

No idea if this is mods related, but other than Orx I have the same set I've used for many months without issue.

KSP version is 1.8.1

Anyone else experienced this or have an idea on how to solve it?