regression in old API tone mapping

When the new tone mapping API was merged, HDR10 tonemapping to bt709 in ffmpeg's vf_libplacebo filter (uses the old API?) regressed and is now bugged (far too dark). This will (presumably) be fixed on ffmpeg's side by switching to the new API, but ffmpeg 5.0 (requires libplacebo version after introduction of bug) is being cut right now with the old API so the bug causing the old API problems will need fixed on libplacebo's side in order to support ffmpeg 5.0 (or the new API snuck in as a bug fix?)