There are two things you need to understand from the Application.targetFrameRate documentation as the document states:
If vsync is set in quality setting,
the target framerate is ignored, and
the vblank interval is used instead.
The vBlankCount property on
qualitysettings can be used to limit
the framerate to half of the screens
refresh rate (60 fps screen can be
limited to 30 fps by setting
vBlankCount to 2)
/targetFrameRate/ is ignored in the
Seems like second one is your issue. So test it on a device as a build.