I've traded 2 sets on Dex for Weapons on Wrath and I used paypal to buy his Fenrir, I got the Fenrir right after I did the payment.
Musk is a good trader, you guys can trust him.
As I said on the previous reply, just to avoid the pet's death! OMG... it is really hard to manage get such a pet like a Great Wolf to 70+ and the possibility of avoid such exp lost is a great thing.
You can mount any pet while in combat, at least on Dex.
The reason for unsummon a pet while in combat would be to avoid his death while pvping clan wars or stronger mobs.
I've tried this on Dex server (lineage.ro).
I've there a Great Wolf lv 71, and if I want to force unsummon while I'm on combat state I just mount it and unmount, done, your Great Wolf or Strider is unsummoned.
I hope it works for everyone. Btw, Dex server is Hellbound l2off