This patch fixes "jumping" vehicles when the new world dialogue is open. The dialogue display routine calls calls karte_t::sync_step, and karte_t::step on every sixth frame. karte_t::step however also calls sync_step via interrupt_check because the last sync_step time is not updated. This patch fixes this behaviour.
This might be related to the fact that opening new world dialogue while playing a network game, guaranteed desync after a while (even if you close the dialog). Same for save and load dialogs.
The desync happens because you are leaving the main loop when the new world dialoge is open and will not be fixed by this patch. Anyway, thanks and incorporated in r 8764