Just to expand on something Don brought to light (and nailed perfectly I might add), when dealing with animals that are wild caught, as many species common in the trade these days are, you also have to worry about bacteria, fungus and other icky microfauna that may be passed between frogs.

A white's tree frog from Indonesia has a much different internal microfauna than a Green Tree Frog from the USA......putting them together into a confined space where they are guaranteed to cross contaminate each other combined with the added stress of being captive will no doubt result in a bad situation for the animals, whether they are short-term or long-term.

In short, like the wise musicians 'The Offspring' once said:

YOU GOTTA KEEP 'EM SEPERATED!