Scroll boxes not working?

Scroll boxes not working?

Hi, when I have a field in which I can select any number of multiple options, the CRM shows the option in a box. I used to be able to use my mouse to scroll through the list and select the options I want. In the last month or so, however, this has stopped working and I can only scroll with the arrows on my keyboard. That makes it impossible to select two items on the list when they are not both visible at the same time. Help!?

Pls see this screen recording to get an idea of what I'm talking about:
https://docs.google.com/file/d/0BzJLU-U642WSSGZfTHp4V1FRZEU/edit?usp=sharing


I'm using a McBook Pro with the latest OS, Chrome as a browser, and am trying both a magic mouse and the trackpad.