We created a solution for this in the past and it seems to have regressed.

So when you start routing from a trace, but want to route on another layer, and your cursor is still within the bounds of the via, you should be able to use the context menu or the hotkey to switch layers and the system will simply switch layers - without spawning a new via.

The regression is that it spawns a new via on top of the original via.

Mihir worked on the solution and is aware of this regression. We discovered it during dogfooding for Release 71, although the regression exists in prod.