On 0.10.9F if you zoom in (left shift plus up) any amount you cannot zoom out (left shift down) to the same level as the game started.
To further explain, if you call the zoom level the game starts as 100% if you zoom in to 110% you cannot zoom out to 100% it will only allow 110%. If you then zoom to 250% you can zoom out back to 110% but not 100%.
To further explain, if you call the zoom level the game starts as 100% if you zoom in to 110% you cannot zoom out to 100% it will only allow 110%. If you then zoom to 250% you can zoom out back to 110% but not 100%.