SD Card issue with deleted items - .trashes

I am puzzled, baffled and confused.

Whilst I am new to the D80, I have considerable experience with all matters photographic and computing.

Most of the time I am using Adobe Lightroom to import and manipulate my shots.

Having used up 75% of my large SD card (am shooting in NEF mode) decided to cull the frames on the card using Adobe Bridge - as it allows me to 'look' inside the card as it would be rather laborious to do it with the D80.

Better mention that all of this is done on a Powerbook using OS X.

So after having deleted a fair number of pictures I was amazed to find that the D80 counter has not increased the available shots.

Took the card out and inspected it (via a card reader) with Finder which revealed a folder called .Trashes within which there is another folder called 502 holding all the deleted items.

So far so good. However, under OS X I can't delete these.

As I suspected I can delete them using Windows Explorer (which revealed that in addition to the picture files there is a matching . DSC_nnnn file - presumable a locking file).

I know that I could delete the lot with Windows or save (again) what I wish to keep and reformat the SD Card in the D80 but...

So the question to you expert folks is this - what am I doing wrong?

Surely this can't be the way one is supposed to work.

Your input will be much appreciated.

Sorry to be a bit verbose but I felt that I ought to give you a complete picture.

Will