Whenever I search for an item using dash it knows the default way of opening it. However if I drag a file into the launcher it can't be added, even if it is executable. For example if you would like minecraft to show up you will have to add a custom launcher, or if you use dash to find a pdf file, you can double click it and it opens evince however you cannot drag it into the launcher.

The animation surrounding this behavior suggests that this was done by design. Why is this useful or necessary? Is it a bug?