When you use the ctrl-w time acceleration, Simutrans kills the frame-rate to about 10FPS in order to avoid overloading the processor. No big deal, I guess it allows Simutrans to be used on weaker systems.
The problem is that FPS throttling also seems to happen when in paused mode too, making scrolling and building rather more difficult. Not majorly so, but enough to be a slightly irritating. This seems rather pointless, as surely the CPU usage drops when the routing pauses?
Again, only a little thing, not really very important.