Invert Records - feature or bug

Hi Guys,
I have an interesting occurrence using Servoy 2.2.5 with mysql databases. I am using Windows XP as my test bed, but I get the same behavior from my production server running on Linux.

Total records in database = 1707
Select-->Find with dept = admin - returns 67 records - so far so good.
Select-->Invert Records returns 1055 records --- OOPS, say what

1055 + 67 = 1122 (short 585 records) does not compute.

Digging around, Mysql stores a NULL in the dept field for those 585 records, since they are empty. It seems that Invert Records is taking my initial find, and selecting those records that are not null - hence the 1055, when I want all the records whether null or not.

Is this a feature - or is it a bug? Or is the answer to switch databases?

Any advice is greatly appreciated.

Thanks
Graham