Turn off all other monitoring software except for RealTemp and see if this glitch is still there. Also make sure you turn off all of your side bar monitoring gadgets when testing.
The main problem is that the monitoring timers in the Intel CPUs are not a protected resource. That means that any monitoring program can come along and change these timers and that can completely screw up other monitoring programs.
Most users like to run a handful of monitoring apps and compare the results but with shared monitoring timers, this isn't such a good idea.
If you run RealTemp by itself and everything is OK, start adding one additional monitoring app at a time until RealTemp goes buggy. This will help you track down what program is abusing your system monitoring timers by randomly stopping or resetting them. I think Intel frowns upon that but they don't do anything at the hardware level to prevent this from happening.