What is an unaccounted tick when profiling with nodejs?

I ran a sample script with --prof and processed the data with the correct version of v8's tickprocessor. In my report, I consistently see:

Code move event for unknown code: 0xb3641e60 Code move event for unknown code: 0xb36b3460 Statistical profiling result from /home/j03m/v8.log, (1418 ticks, 500 unaccounted, 0 excluded).

I understand the concept of a tick and I see inside the source of tickprocessor that an unaccounted tick occurs when a tick has a stack frame which cannot be mapped to anything in the built codemap. What I'm not quite sure of are the why's? Ie, when/why wouldn't something in the stack be found in the code map?

For some additional details, my v8.log was created with node v0.10.26 and my log was processed with linux-tickprocessor v8 3.14.5 on ubuntu.