Ah, I just noticed you are using an Nvidia card (I should read more closely apparently). The Nvidia driver does a funny thing in order to support Nvidia's Dynamic Twin View functions. It basically creates custom timings that make the system report false refresh rates. Your system is actually using the correct refresh rate, as your monitor indicates, but it will show up the Screen Resolution preferences as something weird like 67 Hz or 50 Hz, in your case. You can stop that from happening by adding an option to your xorg.conf to disable Dynamic Twin View. Here's how it is on my system:
Code:
Section "Device"
	Identifier	"Generic Video Card"
	Boardname	"NVIDIA GeForce 7 Series"
	Busid		"PCI:1:0:0"
	Driver		"nvidia"
	Option		"DynamicTwinView"	"false" <---this is the important entry
	Screen	0
	Vendorname	"NVIDIA"
EndSection
With that option set to "false", the system will always report your actual refresh rate. I have found that some games run through Wine can't tolerate the odd refresh rates that Dynamic Twin View creates. However, adding the option will disable some of the monitor configuration functions in the Nvidia control panel. I never really needed them myself, but you might.