Mouse bindings can be triggered during save loading
When you launch a game and start to load a savegame, the whole loading is handled as a part of input update loop from the main menu. This "outer" update continues its execution immediately when loading is finished, so it can trigger actions despite game setup was not finished yet.
Keyboard and controller button presses do not trigger in-game bindings in this case due to
controlsDisabled() check, but mouse buttons can trigger them because this check is missing.