Dragging from the file roller window starts to extract the selected files. If you drop before the files have been extracted, the operations is canceled.

This is a problem, because drag and drop is a very fast movement compared to the time it takes to extract files (when, say, bigger than 1 Mb, which is often). So most of the times the files don't get extracted. If you want the files to be extracted you've got to hold on the mouse button until the progress bar of file roller reaches the end, then drop the files.

If drag and drop worked as expected it would greatly improve user-friendliness !