That sounds very unusual and I cant think of any reason why that would happen.
I was also suprised to hear that after using 30-60 mg's of oxy everyday for several months didn't cause you to experience much more severe withdrawal effects....those arent very high doses, but they certainly arent that small either.
My best guess is that since you have been using oxy for so long, that your tolerance was bound to increase and it was in the process of increasing even more when you decided to take a week off. So when you started using again, your tolerance would have been atleast where it was before, or maybe even slightly higher due to the fact that oxy takes a little while to leave your system, and since your tolerance was in the process of increasing, the break didnt have much of an effect because a week off isnt really that long of a time period...apparently it wasnt long enough to get all the oxy out of your system, allowing your tolerance to start to lower.
this is just speculation, but I can't see any other possibilities. Maybe its some sort of weird placebo effect?...how many times have you used oxy since you started again after the break?