File drag drop motion has been revised. (v184.108.40.206)
1. Drag and drop in Media source list
If you drag and drop in Media source list, it is not added to Timeline but only in Media source list. If you feel uncomfortable with a mixed order to Timeline when you add multiple photos, you can add to Timeline in order after adding in Media source list, and edit much easier.
2. Drag and Drop in Timeline
When you drag and drop in Timeline, it is added to both of Media source list and Timeline.
If it is a file which needs to be added to Timeline directly, try adding it directly to Timeline.