Unmerging breaks event controllers, not just the merge-block controllers, every ec on the grid

I built and configured the attached grid as two separate grids, by hand, no blueprints or anything, in pure vanilla nonexperimental survival apex steam, with validated install files, turned off the lights, merged, they both turned on, unmerged, they both turned off, merged again and it's broken. Sideband testing says it's the unmerge that does it: after the first unmerge the broken event controller still sees its own merge block and has it as "selected" but it's in a different-subgrid color.

The thing is, this isn't the worst symptom, it's just the first one. The unmerge breaks every. single. event. controller. on the damaged subgrid, in a variety of ways, and that variety grows if you're using the creative tools.

p.s. you can *recover* from some of the damage, it's not a workaround because, well, keep reading, grind the damaged ecs to below functional and rebuild them, they then see the devices they have recorded as selected really are the ones they had selected. Do that for every EC on your ship and you'll at least get your ship back. It'll probably help if you make yourself a downgraded grinder, even on realistic grinding the elite one almost wrecks a sg ec in less than a second.