I am not sure about MS/MS but on GC-MS analysis. we have recorded similar kind of observation. We have observed that ephedrine/pseudoephedrine undergo some kind of cyclization and their mass spectrum is no longer observed. instead MS libraries identify it as phemetrazine-a pseuo match. It seems, the probable use of solvents contaminated with formaldehyde results in cyclization in inlet, resulting in formation of cyclic product with mol. mass equal to phenmetrazine but structurally different.similar is true with other derivatives.