Reproduced on Demo, on 4.5.8 and on master

How to reproduce : 

1 - Create a resource and on resource view book this resource for instance on 8 Septembre between 12h30 and 13h30. 

2 - Create an event from 6 to 10 septembre, between 12h30 and 13h30, without resource. 

3 - Update the created event to add it resource, and choose to update all events. 

=> Resource is not available, but it is possible to update event. 

=> Resource is booked twice