I have a large mind-map.
If I zoom to fit to page, I can no longer zoom in. Counter-intuitively, if I zoom out, the image gets bigger (!); it gets magnified to 400%.
My user model if this is that Freeminds is relying on the relative position of 'user defined' zoom in the menus. In other words, 'user defined' is the last ('biggest') entry in the menu. If you ask for 'zoom out' (make smaller), this bumps you up a cell in the menu, so 'user-defined' goes to 400% (interestingly, if you ask for zoom-in at 400% it stops there).