snap zoom to native resolution of background map

[Klumbumbus]

It would be nice if there is an option that the zoom snaps to the native resoultion of the used background imagery. In the context menu of e.g. mapnik tms layer in the layer list there is the option "Zoom to native resolution", but this is just a onetime fix. After the next scroll with the mouse wheel the zoom is "broken" again and the text of a map background unreadable.