gwtchosen select box closes when clicking scrollbar (using IE)

[jehie]

This can be reproduced using IE for example here: http://arcbees.github.io/gwtchosen/

1. Click on the Choose a country box (where you can select multiple) and see the country list open
2. Click on the scrollbar or scroll buttons
3. The scrollbar closes

For some reason this does not happen always, maybe in 80 % of clicks.

This problem occurs with IE9,10 and 11. Works fine with Chrome and Firefox.

[jehie]

Any ideas on this?

Thanks!