Too Short Charged with Ecstasy Possession ... NOT METH

Rapper Too Short dumped ecstasy in the back of a police cruiser following his DUI arrest last month ... NOT meth as cops previously believed ... this according to new legal docs.

TMZ broke the story ... after Too Short lamely tried to flee the scene (see video below) he was charged with possession of a controlled substance believed to be meth, but law enforcement sources now tell us the criminal complaint has been amended to reflect the controlled substance in question was actually MDMA.

But here's the deal ... It doesn't matter to Mr. Short, because his defense is simple -- he didn't have any drugs, and whatever was found in the back of the cruiser must have been left by the previous prisoner.

Prisoners -- they really need to learn to pick up after themselves.