I have noticed that if you give a marker a customName it displays it while in vanilla you are aparently not able to do that.
The same goes for when spectating markers using /spectate.
The /spectate modification is more a minecraft thing because some weird stuff happens when doing the same in vanilla because you get moved but does not really spectate.

The Minecraft bug:
https://bugs.mojang.com/browse/MC-223142

But the name thing is a problem.

Yea, so markers normally are not told to the client that they exist. VB removes that so clients know about markers.

The bug is from /spectate being run server side, so the server knows the marker exists and puts the player at it, but the client doesn't see any entity so it let's you move around, but the server assumes you're still spectating and thinks you should stay put.

I'll fix the name tag thing, the other seems to be intended behaviour, just in a less buggy way.

I think I can fix the name tag bug anyhow.