I'm building a custom fieldtype that uses Assets. So far, I've implemented Assets.Sheet, as described here: http://docs.pixelandtonic.com/assets/developers/sheet.html.
But when the Sheet slides into view, Assets tries to refresh the files, and no files are being shown. There are no JS errors and the thumbnail list is emty (checked the html code). Only a console message from garnish-0.1.min.js saying: "Double-instantiating a select on an element".
The sheet does work properly with any other standard Assets field, but not with my fieldtype.
Here's a screenshot: http://cl.ly/image/3b2D2t1I3g0f
Anybody any idea how to solve this?