If you save a file, the quicksave button on the upper left is greyed out. If you change a formatting of a footer or a header e.g. with a frame in a specific color. The button will not be availible again to save.
Cannot reproduce anymore using Linux Mint 15 x64 with Version: 4.2.0.0.alpha0+ Build ID: 3c8d419f4ba4ea9fa4d00b5691900dae091fd3a (and also 4.0.3) Changing the background color of a frame (background color, border color, ...) etc result in a re-set of the save icon in the toolbar. If you still can reproduce this, please mark this bug as NEW again. Kind regards, Joren