Although I don't have my references handy, I thought that I had read that the M-46 was basically a remanufactured M-26 instead of a new tank based on the previous one. Additionally at the Amazon link below, one can purchase a a book by Stephen Zaloga titled
M26/M46 Pershing Tank 1943-53. I'm not absolutely sure whether Pershing is the official name for the M-46 or not, however, the mistake, if any, seems to have been an honest one.
http://www.amazon.com/exec/obidos/tg/detail/-/1841762024/qid=1100031964/sr=8-13/ref=sr_8_xs_ap_i13_xgl14/002-9318822-2405614?v=glance&s=books&n=507846