Comment 7 for bug 656575

Sigh... then file an RFE/Wishlist bug.

This is *not* a bug, but instead a documented action of both OOo and LibreOffice. Further it is similar to the action of Microsoft Excel:
http://office.microsoft.com/en-us/excel-help/sqrt-HP005209269.aspx
<quote>
Remark
If number is negative, SQRT returns the #NUM! error value.
</quote>
and
<http://office.microsoft.com/en-us/sharepoint-foundation-help/sqrt-function-HA010380036.aspx?CTT=1>
<quote>
Remark
If number is negative, SQRT returns the #NUM! error value.
</quote>

Upstream have already closed your bug once:
http://openoffice.org/bugzilla/show_bug.cgi?id=114981#c2
and will most likely close it again. Again, please file an RFE/Wishlist issue as this is not a "bug" as the program works as documented.