Looks like some textures end up where they shouldn't be when you hover over a track, after the mixer is past a certain "height" - not sure the exact number. This happens only in HiDPI themes I tried (Commala Retina Mod, Default 5.0 and Default 6.0) and has been going on for at least 18 months, so it's not specific to 6.0.
It never really bugged me, as I just reverted back to the regular DPI themes, but 6.0 looks sooo nice in HiDPI and I want to enjoy that very much.
iMac (Retina 4K, 21.5-inch, 2017)
OS: macOS Mojave 10.14.16 (but also happened on High Sierra)
REAPER: 5 and 6, 64-bits
Steps to Reproduce- Open mixer window
- Make it as tall as possible on a HiDPI display
- Hover mouse over arm/monitoring/input buttons
Expected Result
Nice graphical highlight
Actual Result
Textures end up in weird places