Adrian, this may partly explain what you saw:
"Good Plossls are expensive to manufacture, because they require good optical glass and precisely matched concave and convex doublet surfaces to prevent internal reflections. All Plossl oculars are not created equal.
...internally blackened lens barrel with thread baffles is important, as are blackened lens edges and sophisticated anti-reflection multi-coatings. Inexpensive Plossls lacking these features deliver noticeably inferior views and are not a good value.
If well made, Plossls are bright, contrasty, with a flat field, and excellent sharpness."
http://www.chuckhawks.com/common_eyepiece_designs.htm