Zoom lock is changing current zoom
I probably have a different expectation than others (cf. http://help.locusmap.eu/responses/bug_with_locking_the_zoom), but I would expect the Zoom lock button to just lock the current zoom level and not affect the current display.
I have a very detailed Topo map and a high-density screen. Sometimes I want to keep the current detail when zooming out, so I press zoom lock. Now the displayed zoom changes - I can't quite figure out if it's just the "natural resolution" of the current zoom level or another one, but it's very distracting, because I have to manually zoom back to where I was.
In http://help.locusmap.eu/responses/zoom_lock_scale_default_needed it says something about "no need for a setting whether to zoom-in or zoom-out" - that may be correct, but I would really appreciate a setting (config.cfg is ok) to turn off this behaviour completely.