Quote Steve Hill:
Hmmm... just done a quick test. Recorded a mono track centre panned at 0db. Panned it hard left and it played back at +2.9db...
Well, it should be +3dB, but there's only so much resolution in the numbers in the meter, and the meters aren't reading on every sample, they average, so every "sample" of the signal used to redraw the meter probably is averaged over 256-samples or so, causing a slightly innacurate reading, depending on where the meter samples are taken, and what the sample values are - it's like an averaging sample-and-hold circuit. Displaying metering on every sample across all channels would take up significant CPU, which is why is done like this - and Logic always gives priority to audio, and it's metering/GUI priority will fall if the audio needs all the CPU it can get.
Don't forget, Logic's meters *aren't* intended to be highly accurate sample-level displays - they are an indication of levels and track activity. For accurate levels, Logic provides more sophisticated metering plugs, or third party tools such as Inspector XL are invaluable - a good set of meters is a production must, imo. This is true for all DAW's as far as I know.
As for tomafd's mastering thing - don't forget the meters won't show reconstruction overs - it's quite possible to have sample values of significantly less than 0dBFS, and thus Logic's meters won't display overs, but those sample values cause the reconstructed waveform to go over 0dBFS, which was why your mastering guy rejected them.
This is yet another reason to print your mixes with headroom, or at the very least, use decent metering that can handle these sorts of complexities...