Weird behavior with cell layout: table

I tried to create an editor for a simple matrix concept. This matrix concept should contain expressions. The editor uses the table cell layout. For some reason the layout often look very weird like this:

After I close and reopen my root concept in the editor it usually looks as I expected. Is there any reason for this?

Here are my Concepts and Editor definitions. I also uploaded a small example project here: https://github.com/fvollmer/MPSMatrixTest 

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