Utopian reward selection error in contribution.

I've found an error with the way the reward selection drop-down is displaying when you try to select '50/50 SBD/SP' or '100% SP' as your reward,

When clicking the drop-down, instead of the box dropping down, it appears at the top of the page for some odd reason.

The browser I am experiencing this issue with is Google Chrome 62 on a Windows 7 machine.

I've attached an image of the error and have circled the display problem in red so that the error I'm talking about is immediately visible.