Malfunction of conditional formatting in merged cells

Dear Gurus,

Please help me sort out this mystery with conditional formatting malfunction in merged cells (see the attached document). When you select various options from the drop-down lists in Column D, Excel colours the cells wierdly, leaving half of it blank or wrongly coloured. Where the cells have not been merged (Row 9), the colouring works properly. What's the problem and how can that be fixed? Thank you very much in advance!

Agnese