Bugfix #6923:

NLA was calculating extensions of strips in the wrong order. This was not an issue in many cases, although it is highlighted in the following case:

[strip 1 - 'hold' is on] ----------------------------
                               [strip 2        ]

Logically, the end of strip 1 would hold on until the start of strip 2. However, the start of strip 2 was extended to the end of strip 1 instead.

source/blender/blenkernel/intern/action.c

@@ -1071,10 +1071,10 @@ static void do_nla(Object *ob, int blocktype)
 		}
 	}
 	if(strip==NULL) {	/* extend */
-		if(stripfirst)
-			scene_cfra= stripfirst->start;
-		else if(striplast)
+		if(striplast)
 			scene_cfra= striplast->end;
+		else if(stripfirst)
+			scene_cfra= stripfirst->start;
 	}
 	
 	/* and now go over all strips */