Theory : it is well known PMMA can be made accidentally when making MDMA. Therefore, the chemist decides to mix it with MDMA and pass it off. Really, I wonder how the chemist/lab who made these can really live with themselves. And something I've noticed is pills from UK seem to be fake, dodgy or PMA/PMMA combos. This doesn't seem to go on in Germany or Holland, but does seem to go on in the USA a bit also.
Also, recently some legal high research chemical was pressed and sold as Ecstasy. Wham, bunch of people in hospital at a local club event. Police can't do anything. Club can't do anything.
These days a test kit isn't enough, you need to know your source quite well and verify with Pillreports.