Any time I go to create a new circuit, or open an existing circuit, or exit the program, CRUMB asks whether I'm sure, as any unsaved work will be lost. This happens whether or not any work has been done since the last save, which is annoying if I've just saved two seconds ago. Also, since this dialog comes up regardless, it effectively fails to tell me whether I actually have any unsaved work.
The save button is disabled when a circuit has not yet acquired a filename by saving. Most other programs, if they ever disable the save button, it's because there is nothing new to save; in CRUMB, it apparently means the file hasn't even been saved once yet.
I just spent a bit of time building a circuit, and every now and then I'd think, "I should save my work", but since the save icon was disabled, I assumed I'd just saved moments ago and forgot. Then I went to load an example to see how something was built, and of course CRUMB asked me if I was sure. I glanced at the save button, which was disabled, so I thought I had already saved my work and told CRUMB to go ahead and proceed. A few minutes later when I wanted to go back to my circuit, I didn't see it in the load dialog. "What did I name that?" I asked myself. It was then I realized I'd not saved my circuit at all.
Track whether or not the user has made any changes to the circuit since the last load or save operation. Only display the "are you sure / unsaved changes will be lost" message box if there are actually changes that have not yet been saved. Even better, ask "you have unsaved changes. save first?" with options "yes" [invoke the save command], "no" [proceed without saving], and "cancel" [do nothing]; and if saving fails or is cancelled by the user from the save dialog, do not proceed with whatever prompted the question in the first place.
If a circuit does not have a filename because it has not yet been saved, the save button (and its shortcut key) should function exactly the same as the "save as" button. The only time the save command should ever be disabled is if there is nothing new to save.