are there cross braces directly underneath the full wooden top?
if so, this could be an issue since the bottom glass panel sat directly on it.
if the wood warped under the weight and the braces were underneath it could easily create large pressure points that could cause the bottom glass to crack.
generally, it is better if the bottom glass is not directly on that kind of a full top stand. acrylic tanks require this though.
I would look at modifying the stand to make it a perimeter type open top. most stands are built this way and its probably a good method to eliminate the possibilty of pressure points because the bottom glass is then floating anyway.