I have read about the problem and the bug in the following topic.
viewtopic.php?f=15&t=492&p=2312&hilit=spawn#p2312
I use a trick to solve the problem.
I put my own model in the models folder. (e.g. /SoU/mummy).
Then I go to the /data folder and open the default_map_models.cfg file.
I put my model path in the list as shown below.
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mmodel "rc/blue"
mmodel "rc/red" //128
mmodel "rpg/characters/dragon"
mmodel "rpg/characters/golem"
mmodel "rpg/characters/grizzly"
mmodel "rpg/characters/grizzly/lighter"
mmodel "rpg/characters/horse"
mmodel "rpg/characters/horse/black"
mmodel "rpg/characters/horse/grey"
mmodel "rpg/characters/horse/light_brown"
mmodel "rpg/characters/mman"
mmodel "rpg/characters/npcman" //138
mmodel "rpg/characters/rat"
mmodel "rpg/characters/snagon"
mmodel "rpg/characters/wolf"
mmodel "SoU/mummy"
As you can see the number of some models are written as a comment in the right side. The "rpg/characters/npcman" is the the 138th model.
So mine will be 142("SoU/mummy").
Now I open RPG in edit mode. I place my model SoU/mummy from the GUI. As usual it put a model box without a model.
Now I press "." to edit the entity . In command line I can see the following
/entset mapmodel 274 274 142 0 0 0 0 0 0
I just change the second attribute to 142 which is the model number and the next one is the trigger type which I change to 0 (or anything you want according to your requirement of trigger between 0 ..... 29). The first attribute is the Yaw.
/entset mapmodel 274 142 0 0 0 0 0 0 0 0
But still I don't see my model. Now I just put 141 instead of 142 and it works.
/entset mapmodel 274 141 0 0 0 0 0 0 0 0
And now I can see my model appeares in the map.

If you want to use "rpg/characters/npcman" just put 137.
For "rpg/characters/wolf", 140; for "rpg/characters/rat", 138 and so on.
