Start gzdoom with attached zip file with doom2 wad. Start new game. Hold w for several seconds, or any other button which move doomguy forward. Observe warning in console.
Close gzdoom.
Open zip archive, open zscript.zc, comment line 31 and uncomment line 30.
Start gzdoom again and repeat previous steps. Warning in console will not appear.
An addition notes, player "arrow" on automap would disappear as soon as you hit teleportation line for thee first time, in first case scenario.