diff --git a/demos/1.cdgz b/demos/1.cdgz
new file mode 100644
index 00000000..3db56bb2
Binary files /dev/null and b/demos/1.cdgz differ
diff --git a/source/src/main.cpp b/source/src/main.cpp
index 6f5e86e7..3e072c4e 100644
--- a/source/src/main.cpp
+++ b/source/src/main.cpp
@@ -229,9 +229,7 @@ int main(int argc, char **argv)
         SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
         SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, fsaa);
     }
-#if SDL_VERSION_ATLEAST(1, 2, 11)
     if(vsync>=0) SDL_GL_SetAttribute(SDL_GL_SWAP_CONTROL, vsync);
-#endif
 
     int resize = SDL_RESIZABLE;
     #if defined(WIN32) || defined(__APPLE__)
@@ -328,8 +326,6 @@ int main(int argc, char **argv)
     initlog("docs");
     execfile("config/docs.cfg");
 
-    execute("start_game");
-
     initlog("localconnect");
     localconnect();
     changemap("maps/ac_complex");
diff --git a/source/src/savegamedemo.cpp b/source/src/savegamedemo.cpp
index c5ca6f2a..dee3a5a5 100644
--- a/source/src/savegamedemo.cpp
+++ b/source/src/savegamedemo.cpp
@@ -167,6 +167,7 @@ void incomingdemodata(int chan, uchar *buf, int len, bool extras)
         gzput(player1->gunselect);
         gzput(player1->lastattackgun);
         gzputi(player1->gunwait);
+        ASSERT(player1->lastaction == 0 || player1->lastaction-starttime >= 0);
         gzputi(player1->lastaction-starttime);
         gzputi(player1->lastanimswitchtime[0]-starttime);
         gzputi(player1->lastanimswitchtime[1]-starttime);
@@ -316,18 +317,19 @@ void demoplaybackstep()
             target->lastattackgun = gzget();
             target->gunwait = gzgeti();
             target->lastaction = scaletime(gzgeti());
-            target->lastanimswitchtime[0] = scaletime(gzgeti()); // AH,demo
-            target->lastanimswitchtime[1] = scaletime(gzgeti()); // AH,demo
-            loopi(NUMGUNS) { target->ammo[i] = gzget(); target->mag[i] = gzget(); } // AH,demo
+            ASSERT(target->lastaction >= 0);
+            target->lastanimswitchtime[0] = scaletime(gzgeti());
+            target->lastanimswitchtime[1] = scaletime(gzgeti());
+            loopi(NUMGUNS) { target->ammo[i] = gzget(); target->mag[i] = gzget(); }
             uchar flags = gzget();
-            target->akimbo = flags&1 ? true : false; // AH, demo
-            target->reloading = (flags>>1)&1 ? true : false; // AH,demo
-            target->weaponchanging = (flags>>2)&1 ? true : false; //
+            target->akimbo = flags&1 ? true : false;
+            target->reloading = (flags>>1)&1 ? true : false;
+            target->weaponchanging = (flags>>2)&1 ? true : false;
             switch(target->gunselect)
             {
                 case GUN_GRENADE:
-                    target->thrownademillis = scaletime(gzgeti()); // AH,demo
-                    target->inhandnade = gzget() ? (bounceent *)1 : NULL; // AH,demo
+                    target->thrownademillis = scaletime(gzgeti());
+                    target->inhandnade = gzget() ? (bounceent *)1 : NULL;
                     break;
                 case GUN_PISTOL:
                     if(player1->akimbo)
diff --git a/source/src/vertmodel.h b/source/src/vertmodel.h
index 5a57a80e..01da25bb 100644
--- a/source/src/vertmodel.h
+++ b/source/src/vertmodel.h
@@ -14,6 +14,7 @@ struct vertmodel : model
             int time = lastmillis-as.basetime;
             fr1 = (int)(time/as.speed); // round to full frames
             t = (time-fr1*as.speed)/as.speed; // progress of the frame, value from 0.0f to 1.0f
+            ASSERT(t >= 0.0f);
             if(as.anim&ANIM_LOOP)
             {
                 fr1 = fr1%as.range+as.frame;