Kelo,It depends on a whole bunch of factors but even when everything else is the same 2 cuttings can take dramatically different amounts of time to root and you can just bet that when you get the hard to root one out to have a look it will just be forming tiny easily breakable roots!.
Jdsfrance,I've had some luck with the 'stick in the dirt' method later in the year or outside in a cold frame from Feb onwards,the later in the year you do it the better,Feb/March I probably had 20% success rate last year.If you ever have a problem about what to do with your pruned wood in future please let us fellow Europeans know,I'm sure we can arrange to take them off your hands