[mdlug] Why is a blank cell != zero value in OpenOffice-Calc 3.5

[R KANNAN]

OpenOffice Users,

I opened an exiting (from OO 2.2)  spreadsheet in Oo-Calc 3.5 aand found a
lot of #VALUE in cells where I had a formula prodcing perfectly acceptable
numbers. Then I found that some of the cells where I had blanks were
considered by Oo-3.5 to be strings and that is why all these formulas are
failing.

Why is a blank cell considered to have a zero numerical value. Is there a
global setting which does this?

Thanks for any input.