Hello,
I used an electric wrench on a macerator and just after that I also dismantled an electric furnance and an extractor. After that I picked up an extractor and TWO macerators. (and ZERO electric furnances)
So it seems that the electric furnance transformed to the second macerator.
I also installed:
buildcraft 2.2.12
computercraft 1.21
redpower 2.0pr4d
I haven't had time to build a new electric furnance and to try to transform it again, but maybe I'll post again in the next few days.