This behavior is repeatable. You can test it with a short program that blinks the on board LED. Make change by varying the rate.
Using Dev, if you don’t save changes to a program, those changes are not included in the next compile and upload. If you watch the directory with Finder, you will see the firmware being created. The Success! message will appear in Dev. If you upload that firmware you can watch Finder as it is removed from the folder. Dev announces that upload has started. Core flashes all appropriate colors and restarts. BUT, none of the changes you just made are in the core.
All the steps that Dev would make when properly compiling and uploading are made. Core behaves as it should, but new program is not uploaded.
Hit File -> Save and then Compile and Upload, and now the changes are uploaded into the core.
In Build, the compile and upload are grayed out until the file is saved and the blue circle changed to an x. In Dev there is no warning, help or prevention, just hidden failure to upload.
Some programs won’t let you do things until you save, others automatically save when you do things (Xcode for example). This is the first program I’ve worked with that pretends to let you do something but actually does not until you save changes. Can be confusing…