What is in these cells?

Often when trying to get formula to work, or indeed VBa code, there are unexpected results returned, apparently empty cells are not empty at all, but what is in them?

The cells are not so obviously "used cells"

The attached workbook illustrates my dilemma.

I put a formula in Column A, dragged it down, then Copied it and used Paste Special > Values to Column D

If in the VBa Immediate Pane you try

? Range("D" & Rows.Count).End(xlUp).Row

the returned value is 22, but D22 is apparently empty, this phenomenon is often highlighted by using

ActiveSheet.UsedRange.Select

I have tried all the formula I can think of to find what is in the cell and the results are in the attached.

Select any of the yellow cells and press Delete and see the changes.

Can someone explain what is going on?

Cheers
Alistair