cell resizing

Whenever I have cells with wrapped text and the cell is too small to show all the text, normally I highlight the entire row or column and double click the edge and excel automatically resizes the highlighted cells so they are all the right size to display the text.

I am altering an existing spreadsheet someone else has started and the I have a problem. whenever I do the above method to resize a row or column to display the text ....... the cells actually resize down and do not display all the text. I notic as I do each row they are resizing to different heights and I cant figure out why.

I just realized that the rows have a merged cell in them. as a test I unmerged the cells and my method seems to work fine now. Are the merged cells actually affecting this?