Hhmm, but I do see that when I move the VP of one box, all the other boxes that I've made are being edited at the same time, as if they were clones, almost.Yes, that is a beautiful thing about the 3D box tool. You can make a whole bunch of boxes share the same vanishing points and (implicit) eyeline, and then easily change your mind about what perspective you want on the whole scene -- fantastic! It's kinduva a sadly underappreciated tool, I think, unless there's much better documentation on it than I've found (most youtubers are using it to, well, draw boxes rather than quickly solve perspective problems). Maybe you have to have done perspective the hard way with a T-square to really see the value; presumably the author of the tool did.
I'm not sure if that's expected, or if there's a setting somewhere that needs to be fixed.
For me Shift-drag on vanishing point works as expected.
To detach selected boxes from perspective stack and unshare vanishing points you can move them with :sel: Selection tool (F1).
Well, that's an interesting clue. When I F1 and move one of the boxes, as soon as I release the mouse at the end of the drag operation, that box gets transported to outerspace (far outside the page).That's a weird behavior indeed. I'm really curious to take a look at before and after SVGs, if you can provide them.
Tool settings identical to yours. Good idea to try turning off snap, but it made no difference. Making the before/after svg now...
What's your tool settings say?
Does it happen with snapping disabled (Shift+5)?
OK, will try resetting my preferences (after saving). Surely I've messed something up in some innovative way.I just managed to reproduce it! I'm still not sure what's causing it, but it seems like a bug to me.
Fits the hypothesis that the code is picking the wrong coordinate system.I've come to the same conclusion and updated my message with some details (https://forum.inkscapecommunity.com/index.php?topic=1667.msg11048#msg11048).