When I delete pictures, the develop module does not work anymore. One of the deleted picture is shown and no further interaction makes the develop module operative again. LR must be stopped and restarted, then it works again. This behaviour is to be considered as a bug, it did not occur in 6.7 . I hope for a soon bug fix. Thanks
This bug has been acknowledged by Adobe, and will hopefully be fixed in the next update.
The workaround is to delete files in the Library.
This is a known bug. Delete the photos from the Library Module and not from the Develop Module.
Thanks a lot !