Does GIMP's Preserve Luminosity option actually keep brightness stable in Color Balance?

I'm color-grading a set of 8-bit RGB photos in GIMP 2.10 and rely on the Color Balance tool's Preserve Luminosity checkbox to shift tones without changing perceived brightness. The documentation marks this option as experimental, and I've read that the algorithm changed in the 2.99 development series, which makes me unsure how much I can trust it for consistent results.

My specific concern: when I make large mid-tone adjustments with the option enabled, the histogram's peak still seems to move slightly, and I'm not sure whether that's expected behavior, a bit-depth artifact, or a sign the option only approximates luminance preservation. I also need results that survive a future upgrade, so the reported differences between 2.10.x and 2.99.x matter to me.

Does Preserve Luminosity guarantee a stable luminance histogram, or is some peak drift (a few percent) considered normal? Is the 2.99.x algorithm measurably better at avoiding mid-tone shifts, and are there edge artifacts I should watch for? Given the experimental status, is it safer to preserve luminosity manually via layer modes instead?