top under 5.3-RELEASE

I realize this is not strictly pertaining to -CURRENT (though I
suspect it may pertain), but I've noticed a change in the output of
top that I don't really understand.

Through 5.2.1-RELEASE I've been accustomed to seeing the top few
processes using a % of cpu that correspondes to the % free cpu value
in the header part of the output.  Ie, if the machine is 20% idle I
expect to see the process %s to add up to roughly 80%.  This seems no
longer to be the case under 5.3-RELEASE and I'm rather confused by a
0% idle statement with the process %s adding up to only about 15% or
so.

The amount jumps around a bit and seems to bear the relationship I
expect when there is light load, but it looks completely wrong to me
when there is heavy load (as in compiling a port).

Can anyone explain this seeming inconsistency to me?

Sean