I have only tested Wii Play on my new build because I wanted to be able to do "Find Mii" with my own Miis (6502 had a black screen at a part in that mode). I just haven't tested with my own build on enough games to really compare to the regular 5.0 builds, although I still suspected that the frame 0 desync message specifically was usually related to my build. I will get back to you when I get a chance to test Wii Play with 5.0-546, which is the one I have been using for Wii remotes without save files. One last thing I should mention is that on 5.0-292 (another build I tried online), I was never able to get netplay to work properly on Kirby's Return to Dream Land because I would get the frame 0 desync message, and the game actually was desynched online. On my new save build, I was able to get no frame 0 desynch message, but my build is slightly newer, and I also haven't tested enough to see if it really was in sync. I will need to test this a little more.
On 6502, Kirby has no problems for netplay, although 3/4 player doesn't work, which it might on my newer build.
On 6502, Kirby has no problems for netplay, although 3/4 player doesn't work, which it might on my newer build.