It's a (known) bug, although I can't find the bug report right now. AFAIK the bug has been there since EPi 7 beta and is still present in 7.1.

When I had something similar I had missed to deploy the app_browser folder. Could this be it?

Thank you Alf, that suggestion fixed my similar issue:

http://world.episerver.com/Modules/Forum/Pages/Thread.aspx?id=74593&epslanguage=en

We don't have an app_browser folder at all actually. And this problem occur in every browser so I don't see why this would be a problem. But please enlighten me if I'm wrong :)

EDIT: Ok, I just added App_Browser again and that fixed the problem. So thank you! Even if I have no idea why.... :)

Isn't App_Browser for server-side browser detection? Why is anything using browser detection instead of feature detection in this day and age?

The reason why we use server side detection is that this (and a few other UI:s) were written shortly after the release of .NET 2.0. As you might know, most of the editorial UI was rewritten for the EPiServer 7 release, but we still have a few (and descreasing) number of legacy dialogs that still use the theming support in .NET.

We have the App_Browser in our project, but that still doesn't fix the issue for us

Is there something else we might need to do?

Also, could this be the reason why Preview Mode also is broken for us with the scroll bar not updating properly (in chrome).

Copied a folder from another project and now it works.