$input->get not working on Mac Safari/Chrome

[cjx2240]

I've got a basic form with method="get"

I use $input->get to retrieve the category, and show a list of pages based on this result. Works fine on PC, and on Mac Firefox.

However on Safari and Chrome for Mac, I get nothing. If I try to var_dump($input->get), I get a white page, even if debug is enabled.

It also works fine with $input->post

Why does this work on one browser and not another, can anyone help please?