I created a solid (from joined surface, which came from a mesh converted to surfaces), then mirrored it, color-coded it, and then drew a solid tube/cylinder shape beneath and not touching the geometry. I then centered the the solid and then used the split tool.

It was taking a long time, so i tried to UNDO. Undo asked me if i wanted to continue with the undo operation. I hit YES, and then it looked as if i were trying to undo. I hit undo again (Ctrl+Z), and this cycle went on and on.

Can it be possible that whatever undo is trying to undo, that it offers an option to "garbage collect" and unlink and delete a selected geometry? It would be nice if UNDO has a progress indicator for complex UNDO operations.