I'm most concerned about this because it is inconsistant. 

Twice so far I've dropped suddenly from 1500+ Silver to below 1000 silver after losing a battle and running out of engery when exploring.  This has not happened every time one of my pets was out of engery and needed to leave the map. Only twice out of about a dozen. I failed to get before and after screen shots as it was completely unexpected each time it happened.  

Edit-- I have lost more silver between leaving the site for a few hours and coming back. So now I don't think this has anything to do with exploration. I'll edit again if it happens again and post any clues...

I'm on Windows 7 using Maxthon Cloud Browser (Webkit).