As the creator of that map I'm obliged to check the problem. I'm afraid I can't reproduce it! I'm using the
latest dev build of ZDoom. On heading outside, you get the cutscene telling you where to go, which you can abort with any of the movement keys - then all you have to do is turn to the right and walk around the house a bit to grab the SSG. Once you've gotten that, the elf's hideout will become accessible.
One word of warning regarding the dev builds: currently slopes and skyboxes are broken. So you might run into other issues with the map(s).