Actual line spacing glitch?

[Wendywhile]

Hi all,

I know there are a lot of ins and outs in getting the line spacing just right in Word 2007, even when you think youve done it all correctly.
However i really feel like i have done it all correctly and the problem persists.
The problem is most evident perhaps only because i am using a full size watermark of lined paper that i created in Adobe Illustrator.
It is accurately ruled every 14mm (approx 40pt). Then exported as png and used as a watermark image at 100%.
I have checked in the word ruler to make sure no scaling has occurrd and all is fine.
The text is 40pt, the spacing before an after is set to 0 and the line spacing is set to "exactly" 40pt. All looks perfect until you hit the second half of the page and you notice that each line of text creeps down ever so slightly, that by the last line the text has dropped down considerably below the line.
I have doubled checked everything multiple times a day for the last week and cannot for the life of me figure it out!
Im wondering if because most wouldnt print on lined paper, perhaps no one has ever noticed this problem?
I have recreated my lined template from scratch again to check it was precise.
Please help!