Max Framerate slider makes FPS lower than set

When I set Max Framerate slider to 60 FPS, I get around 40 maximum (according to F3).
When I set it to UNLIMITED, I get 60 FPS.

Seems like it's setting lower rate than slider states?

All test are with VSync: ON, Windowed mode (maximized window) and Fullscreen. I get around 150 FPS when VSync is OFF, so computer should be capable.