It is outside of our control for how long the game is unresponsive while you switch screen modes, it completely depends on SDL and your OpenGL driver. If that unresponsiveness still causes prolonged wrong lag-o-meters or even real lag with 0.4 clients on a 0.4 server (which has new timer syncing code), send a debug recording.
(No, that doesn't mean I don't care for 0.2.8 problems, but I don't want to go around fixing old problems in old code and risk breaking new code in the process.)