How Is This Possible?

[Spishkey]

went out this morning, came back three hours later to find my fish room, bathroom and kitchen floors flooded.
my oscar tank sump has seemingly emptied its contents onto the floor!

the sump is totally empty, meaning the pump and 2 heaters are knackered (pump ran dry, heater blown)

what i dont understand is the tank above is also half empty? how has water managed to get out of the main tank? (no leaks no cracks in the main aquarium, just a huge burst in the sump!) the water is pumped from the sump into the tank, and exits the tank via a ridge/overflow into a seperate compartment on the tank, this then emptys down a spout into the sump.
so...how did the water escape the tank??? its just not possible surely? the overflow compartment is still full, and ive since refilled the main tank (to just below the overflow level so it doesnt run into the sump)

answers on a postcard please................im stumped, totally!

also another quick question, is it likely my stand is knackered now? its made from wood and is soaked completely at the bottom..............

 

[Curiosity101]

The only thing I can think of is that there is a leak in the overflow somewhere, possibly just above where the water level was in the main tank when you got home?

If I remember correctly the over flow 'box' is basically like a square insert that is attached to an inside corner of the tank? Has a comb on the top, and the water 'overflows' over the top of it? So there is presumably a chance that it isn't properly sealed to the tank?