What I usually do is do a Find/Replace on the source sheet Finding "=" (without the quotes) and Replacing With "'=" (w/o double but with single quote) which turns all the formulas into text. Then copy and paste, and reverse the Find/Replace to turn back into formulas.
I must admit I had problems with it too - so much so I now replace + with #= which Excel seems to have no problem recognising the replacement as text.
Anyway, that doesn't help you now. Try selecting youyr formulas and going Format>Cells and changing to Text format and now replacing '= with = You will then have to convert the cells back to eg General format and then do a Find/Replace with = for = to convert back to actual formuals. Hopefully this will work - post back if not and we'll try something else.