There have been many heated discussions concerning the Mac OS 8.6 startup resolution-switching problem on this forum, and I have seen no specific workarounds. But after installing Mac OS 9 on a DIFFERENT hard drive and using it for a while, then going back to the drive with 8.6, the resolution no longer changes during startup! I am elated by this development, as the res-switching problem has fried one monitor and damaged another.
The only other thing I have done different is install ColorSync 2.6.1 into Mac OS 8.6 that I downloaded from Apple. I did this the same day I switched back to 8.6 because this version was newer than the one installed by 8.6. I configured ColorSync to my needs and never noticed whether or not the res-switching problem still occurred, as I seldom sit and watch the startup process anymore.
Mac OS 9 does not have the res-switching problem, and I wonder if some sort of cross-pollenation has occurred between it and 8.6. Could it be that Apple has quietly fixed this "normal" startup problem with ColorSync 2.6.1? I certainly wish I could bill Apple for the fried monitor and for the repairs on the other damaged one caused by this "normal" behavior. Is apple quietly saying "oops!"?
My setup is this: Yosemite G3/400 with 16 MB Rage 128 card and a 17-inch KDS VS-7 monitor. I also can connect an AppleVision 1710 (no AV) to this machine and have the same results - no res-switching - FINALLY!! I configured ColorSync with the "Multiple Scan Display" system profile, "Epson Stylus Color 740 Standard" RGB default, and the CMYK default as "ColorMatch 3.01 - SWOP Ink, Sheetfed, Coated". The preferred CMM is "Automatic". The only startup anomaly I notice is a slight gamma change during the process, which is needed anyway.
Whatever the reason, I'm glad the problem is gone in my 8.6. I bought OS 9 for the sole reason that it did not have the startup res-switching problem, now I am stuck with 8.6 called OS 9 with multi-user functionality and voice passwords. Too bad I can't return it since it's been opened! I hope this discussion will help those of you with the "normal" problem so you don't end up frying a monitor like me. Post whether or not this works for you...I'd love to hear about it!