OK, I see it is the selection shading rather than the applied shading. You are seeing the shaded area of where the paragraph in the cell is sitting. The first columns have 12pt text while the next columns have 10pt text. Generally both these don't have paragraph spacing above or below so the smaller text cells take up less vertical space than the 12pt cells.

The table is mainly using auto row heights so the tallest paragraph determines how tall the row is. If the row is autoheight then at least one of the rows will be fully shaded. The first row is set to "At Least" greater than the paragraphs inside it so the selection shading sits at the top of the cells in that row.

In the case of the 5th row, the 3rd cell has space above/below added to the paragraph so it is taller than in earlier rows.

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Andrew Lockton
Chrysalis Design, Melbourne Australia