What happened is you copied a cell from a header and pasted it elsewhere into the table. It copied the contents of the cell including the formatting, just as it should. You can change the cell fill color and borders back to how they were (the procedures are covered in the User's Manual). Or you can select the table, go to the sidebar, click on the triangle to the right of "blue headers", and select "clear and apply style". This will clear all user-added formatting from the table and put it back to the template default.
Sorry, but I don't understand what you just said; however, it no longer makes any difference. Somehow, the thing seems to have fixed itself, and that "bad" cell is no longer there. It is the Christmas season, after all. On the other hand, I couldn't leave well enough alone, and when I tried to add one more blank row elsewhere, almost the same thing happened. In this new case, a singers's name moved from where it belonged to the column to the right, where it doesn't belong. I'm going to settle for that and put the table to bed. Thanks for your help.