Completed Goldrust with only 26000 points
Windows 7 64bit
8GB RAM
Intel i7
Nvidia GTX 750 Ti
Version v1.6.66f3
Got a victory screen after amassing 26000-27000 points despite Goldrust requiring at least 75000 points to be completed.
It should be noteworthy that I tossed 3 level 5 heroes into my dungeon and got the completed screen after they were killed. I also did NOT get the Working-Class Hero achievement.
Unfortunately I have not been able to replicate this issue and as far as I can see there doesn't appear to be anything that stands out in the output log. I don't suppose you happen to have a save just before or after the issue occured?