Are you using Dreamweaver 8? If so this is normal behaviour and it doesnt affect the total number of lines available. The reason Dreamweaver does this to help you not have to scroll horizontally if a line gets too large. The lines are still the same just that some lines are taller than others.
You can Stop DW8 from doing this by going to View -> Code View Options and deselect Word Wrap DW8 should disply your code normally rather than having like:
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