cell contents disappear and reappear

[excellence]

This is a small portion of an address list, where each address has the ability to have for 2 names.

Why is it that perhaps 95% of the time if the lower cell for any given address is empty and I want to fill it in (could be in any of the columns C thru F), as the contents get entered in the lower cell, the cell above it immediately vanishes as I start typing in the lower cell and then reappears after I enter the contents in the lower cell? What reappears is what vanished, so I haven't lost data.
It just seems odd.
There are no formulas in this document and figured it is some formatting issue that I can't seem to find.

Thanks

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[LazyBug]

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