Misreported memory

I recently bought 2x 256meg PC133 memory modules.
When I installed them they reported that each was 128megs. I tried in 3 diffrent machines, a P1, P2(400Mhz) and a P3(1Ghz). The 128meg that showed up on each tested out perfect, just that the top 128 did not exist.
I took the offending back to the store just to be told that the specfic make did not like anything below 1Ghz, (fair enough).
I had the shop try it in his machine, a P4(2Ghz) and the thing just went crackers.
The shop was still quite happy to replace.
has anybody expereinced anything like this?