It's not just your problem. Have a look at my graphs in my thread here
http://www.rc-monster.com/forum/showthread.php?t=12049. They show the same 60000rpm spikes. If you zoom in on your graphs the rpm sensor is fairly accurate when the motor is spinning under power. It look like it goes to 60000 possibly under brakes (proportional breaking probably throws it off).
Savage: FLM Conversion, 6s, MMM, CC 1520.
Mini-T Pro: Micro Pro 6800kv, Lipo, HS-81mg, Dirt Hawgs
M18MT: Quark 33A, Y22S 6000kv, FP 2s Lipo
LRP S8-BX: RC-M Conversion, Tekin RX8 B1600KV, 6S.