Since your monitor is a CRT and its EDID does not specify a preferred mode, neither randr nor the driver know which mode you want as the default.  Some users prefer 1024x768, others prefer 1280x1024, etc.  Setting a preferred mode in your xorg.conf is the correct fix.

That said, I suppose the randr core code should prefer modes from the detailed timing block of the edid over other modes when picking a default if there is no preferred mode defined.  That would need to be fixed in the xserver, not the driver.  Open a bug against the xserver.