Hi,
Unfortunately that is the correct layout in that case. The script we are using to display a multiselect search drop-down layouts does not support all the mobile browsers yet: https://harvesthq.github.io/chosen/
This is unfortunately the best script on the market, this has the most extensive mobile support.
Hopefully they can develop a solution soon to support all non-webkit mobile browsers, until then, the default “multiselect” drop-downs are displayed.