I found the plastic circlips to be a pita and now use the original pedals without the plastic circlip.

When put the pedals on, I take real care to make sure that the collet (sliding ring) snaps right back into place.
When they were new it was necessary to push the pedals in firmly to compress the O ring so that the collet did not hang up in a part locking position.

I had problems a couple of times initially with my first and narrowest set AR2 EZY but the problems seemed to go away. I'm not sure to what extent thats due to the care I take or because I now have Power Grips on them "http://www.amazon.com/Power-Grips-Sport-Pre-Assembled-Strap/dp/B001FYGGLC" which keep my foot well clear of the collet. "Clipless" pedals would do the same.

My other EZY pedals are wider and have not been a problem without Power Grips.