The choices are Daily / Weekly / Monthly,
Weekly wouldn't work since I want a backup done daily. So unfortunately there is no way to have certain days excluded. Either way that work around would be risky, if for some reason a machine was turned off one night I wouldn't want weeks to go by before someone notices the backup has been paused.
FTP log is empty, obviously used for the built-in FTP server which I have turned off.
Weekly WILL work - setup five weekly schedules, the first to run on a Monday, the second on Tuesday, etc., - tedious maybe, but it works - and yes the onus is on you to make sure your backup target is on and available.
There are alternatives, you can purchase a backup solution that runs on the PC and writes to the NAS, in which case you'll still have to make sure that the NAS is on and available, and that the PC did in fact backup - at least doing it from the NAS you can look at one screen, once a day, and at a glance, you can see which backups did not run.
Backup solutions can be created that will largely eliminate the human factor, but, the more you automate it, the more it will cost you, and at the end of the day, your network administrator still needs to verify that it all works - or risk loss of data.
One of my clients has two racks full of servers, plus a robotic tape system to back them up, but he still has to do weekly test restores to verify that the system works.
And just my opinion, but it's not a bug - it works the way D-Link designed it to, it may not be what you want, or have the features that you think are necessary, but it's how they designed it, and it does work.