I've found on Tetrahedron Lett. 38, (1997), 7276 a method for the cleavage of oximes to carbonyl compounds using Mn(OAc)3 in benzene under reflux.
Globally:
2R2C=NOH + 2Mn(OAc)3 =(benzene)=> 2R2CO + 2Mn(OAc)2(ppt) + 2AcOH + N2
Yields are guaranteed between 86 and 96%. Time of reflux between 30 min. and 2 h.
Other methods of cleavage:
JOC 51, (1986), 3063 (using CTAP = cetyltrimetylammonium permanganate)
Tetrahedron Lett. (1971), 195 (using Ti3+)
JOC 31, (1966), 3446 (using bisulphite)