True Edward ... had to find an appropriate answer ... or in fact, I have/had one, but you may not like it that much.
In the later versions -which exactly I can't tell- had slipped in some debug code for this matter. So, this was active in production unintendedly.
This debug code did just *not* activate Invert, but the math to correct a 2 byte positive integer (as what is used in Redbook) while half of it represents negative (volts), was still active but now wrongly applied. In fact, with Invert the lot was DSPd a bit ... and certainly did not invert the phase.
Now it is working properly, and what you might perceive from it is untouched data, whereas before it was mangled with (though unintended). So now the phase is just inverted, nothing else. So what you are dealing with now is that maybe you have to learn how to hear the difference.
But careful now ...
The Phase Inversion, though originally setup to satisfy those who are disturbed by wrong absolute phase, when finished was not officially implemented at first because of the perceived idea of it not being useful because it hardly occurs that a whole song is recorded with wrong absolute phase, and merely individual elements (singer, guitar, the snare drum) are. However :
When the Q1 was introduced, it occurred that at certain "levels" of Q1, now Invert suddenly could make the difference of the world. Btw, this was when the bug as described above did not get into the production version yet.
Moral : When Q1 starts to be, say, nasty, it is exactly the point where Phase Invert will drop your jaw. That is, it looks like the general experience from people; not only my own. This phenomenon by itself implies that there are also Q1 settings where Invert hardly makes a difference (think of +90 vs. -90 degrees).
Phase is the most important phenomenon within audio IMO. Not so much to the sense of "proper phase" but far more in the area of properly aligned.
