Box blur effect bug (?)

Dear JB and friends,

There is a very small bug with box blug, which can be reproduced easily.

Create a movie in PAL.
Box blug the whole image, with 20 boxes.

Export in full PAL resolution, there is 20 boxes.
Export at 320x240 using custom options, there is less or more than 20 boxes.

Conclusion: the number of boxes in box blur export is linked to the export resolution during rendering.
Strange. Is this a bug?

Kind regards,