The compound is porous and has absorbed more of the paint than the other areas. People prime first to even the field before painting but newer premium paints work better to eliminate that step to avoid what's called flashing. Always ask, research or test under various lighting conditions first as it depends. Probably safer and easier to just prime. (I did try not priming a good sized patch, using BM Aura Matte paint, and cannot see it. I simply applied another coat of the Aura over, but it might take two in some cases. Holds up to grazing with a light but this area does not see the light of day! I was surprised but it worked well on a wall that already had two coats of fresh paint. Why did you use drywall compound on seams and nail holes? Caulk is used for seams (get a high quality flex elastomeric like Dynaflex 230 or BM Crown & Trim to reduce the potential for cracking). Wood filler is used for nail holes. There are some differences to working with MDF rather than wood but I don't know what they are.

I just did Paintguy's method a couple weeks ago when our entry was painted! He described (on a recent thread here somewhere) using a screw right next to the nail to pull the nail back in with the underside of the screw-head. A couple of MY nail-bumps (out of 6 in the same corner!) were 10'+ up on our high entry wall...right next to the front wall which we weren't gonna paint yet! Had to be carefull not to nick that front wall. * After a couple spackle-fills and rounds of flush-sanding, I wiped all the sanding dust off the clean wall. * Had to use painters-tape & plastic to cover-up the adjacent wall cuz I had to shoot some spray-texture over these spots. * When spray-tex was dry, I lightly brushed a hazy coat of primer over these spots, then turned the project over to the painter coming the next day! All they had to do now was roll the Gray C2-One primer & 2 coats of Matte Paint. * I must've done a good job! Can't even tell where I did repairs on that wall... Faron

Knockdown is easy to duplicate ... try the technique on some scraps of cardboard first. Dilute some drywall mud until it is the texture of sour cream - holds a nice peak. NEED: drywall mud, big coarse sponge, WIDE (10in or larger) drywall blade, clean cloth. Spread a bit of the compound onto a damp coarse sponge. Dab it on the wall where you need texture in an irregular pattern - repeat until the area is covered with peaks of mud alternating with some open areas. When the peaks are stiffening, but not dry (stiff pie dough texture), draw the drywall blade across the patch in one quick scrape. Hold the knife at about a 45-degree angle. Knock the peaks down! Wipe the blade clean between scrapes. The harder you push the blade against the wall the thinner and flatter the knockdown will be. Let it dry, prime it with drywall primer, and paint it. IMPORTANT: Overlap into the already textured area by a foot or more, fading out erratically, and even create some random clouds of new texture. You need to break up the outline of the bald spot.

Use one or two deck screws to pull in the offending fastener - then it will not come out. I say "deck screws" with star drives as opposed to drywall screws because it takes a lot of torque to do this and drywall screws will strip or snap off. See the link below for more details. Here is a link that might be useful: How To Fix Drywall Nail Pops