Cell Merging Custom Sample is broken

[ChronosSF]

If you keep clicking on merged cells, you eventually get a broken grid:

[ChronosSF]

I get this might be super convoluted to reproduce and fix but the sample doesn't have to be so complex. If you are showing how to customize the merging result, you can do so with only one merged column. I doubt the UX of multiple merged columns breaking on selection is even remotely good enough for a working application to use anyway. Having the scenario shown like that, tbh as an end user not knowing the exact way this should behave, I'd be flabbergasted even after a few clicks (without even getting to the completely broken case).