I have had a similar experience which tells me (as others have stated) that a paint "cleanser" is an important step - at least once or twice per year. I had a white Santa Fe. I washed, then clayed and then corrected (multiple passes) with Meguiars' Ultimate Compound and yellow (aggressive) LCS pads. The next weekend I washed again and used XMT 360 for a next to final step before Poorboy's EX-P. XMT 360 gives minor correction, paint "cleanser" action and sealant (kind of like an "all in one"). The orange pad I used with the XMT was filthy (off of a white car) so the polish/cleanser component was removing "something" other than residual Ultimate Compound. I was really quite surprised. I even did two panels with Meguiars' 205 after the UC just to try to "up" the correction but decided it was not necessary. Even on those panels the XMT 360 pads picked up a lot of black/grey "stuff". Really opened my eyes on the chemical paint "cleansers". This vehicle had not had any real paint "treatment" of any kind for a good 2 - 3 years plus - other than being kept very clean with regular washings (but no claying). So, in retrospect adding a paint cleanser step makes some sense - at least once or twice per year. I'll know more in the Spring when I hit it again - maybe with Pinnacle Paint Cleanser just to see what I get. Live and Learn!!
Best Regards,
Martin