Originally by kaihuener

The Drag and drop wrapper only takes dropped files 'sometimes' with Valo theme (Chrome 36.0, Firefox 30.0, IE 11). With Reindeer theme, all works fine.
Demo: see https://www.corporate-data-league.ch, login with given credentials, go to 'Start import', try to drag and drop any file to the pane.
Symptom: The cursor start to 'blink', the drop pane takes the dropped content only very few times, but in these few cases, all works fine.
The code of the drop component is attached, very standard implementation, nothing special.
Again: With Reindeer (same component code), all is fine.

Thank you guys for your great work,
kai

Imported from https://dev.vaadin.com/ issue #14343