It's being talked about on the housing forums but I want to bring this over here, too, because some clarification on it would be really, really nice:

An issue wherein placing a tabletop aquarium on top of another furnishing and then repositioning that furnishing allows the aquarium to clip through other aquariums.
* We strongly advise all players to avoid trying to replicate this issue. All furnishings, including aquariums, that are overlapping or clipping may be permanently deleted when the fix for this issue is implemented.
Now, on first read, it sounds like "don't clip your aquariums or you might lose them" and eh, okay.

But All furnishings, including aquariums, that are overlapping or clipping may be permanently deleted when the fix for this issue is implemented. is very ambiguous and could be taken to mean any clipped furniture, and... well, there goes 90% of the housing in the game?