What was happening if you provided the correct username and password to an autodetected foscam camera? Would it accept the username and password and then say "unable to connect"?
Would you mind testing with one of your cameras to see if it still fails to work? We have made some fixes to the foscam driver along the way, and it's possible that the auto-detected variants will work now.
To test, delete one of the disabled cameras, let it be auto-detected, and supply the credentials. If it fails to connect, please use "Report Bug" from the home settings soon after trying it, and check the checkboxes to upload logs and settings from your device, so that we can see what happened.
Re: blacklist ... How would your blacklist of devices to ignore be different from the list of disabled devices we have now? You'd need a way to display the list of ignored devices and delete entries from it ... Our list of disabled devices is basically that blacklist. (While a device is disabled it is ignored completely -- it not probed or anything else, in addition to being hidden from view unless you ask to see it.)
We probably suggested the wrong thing by using a "trash can" icon. We actually call the action "forget" in the mouseover tooltip. Disabling a device is blacklisting it. Using the trashcan is forgetting any state associated with it -- which means it's taken off the blacklist and, if it happens to be on the network, it's rediscovered.
Re: Synology ... It's almost certainly showing up because your Synology still has something listening on port 554. I own two synology NASes that are not running video station, and they do not show up. If you can ensure that nothing is listening on port 554 it should stay gone after you "delete" it.
(Btw, since you may run into this: the most recent update introduced a bug in the "delete" action such that the deleted entry won't immediately disappear when you delete, but will be gone only after you refresh the page. We'll be fixing that in the next update.)