If you have a blank file opened and type anything, the tab's icon should change color (to red) to show that it has been modified. If you try to save, then cancel out, the icon changes back to it's normal color (blue) and will not change back to red if you make any more modifications. The same thing happens if you open a file, modify it, then go to Save As and cancel out. I'm using Notepad++ v3.9.
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If you have a blank file opened and type anything, the tab's icon should change color (to red) to show that it has been modified. If you try to save, then cancel out, the icon changes back to it's normal color (blue) and will not change back to red if you make any more modifications. The same thing happens if you open a file, modify it, then go to Save As and cancel out. I'm using Notepad++ v3.9.
I can confirm the same behavior in v3.9.
Otherwise, amazing app - love it.
It is fixed in v4.0
Don