Green spot (probably lensflare) in the exact mid of a picture

I have a question and some of you might know.

When I take pictures on a white background isolate the main subject, I always see a greenish spot right in the middle of the frame. It probably is a reflection in the lens due to lensflare and it occurs with all the lenses I have. Or is it a typical issue with the a850

The background is white and lighted by 2 softboxes (2 stops above the metering of the main subject).

The lens flare is very hard to remove in PS.

It looks like flare comming of the white background. I tried shims and masking the main subject with black boards. It just doesn't help

When I don't light the background, it just doesn't occur.

I dont have a clue how to prevent is, do you?????

\Iggy