A bug in Graph display?

I'm using Igor Pro 6.22A on Mac OS X 10.6.8. A strange behavior in "Modify Axis" setting is that when I used the unit with \U in the label, the preview of the label shows the unit as "MS" instead of the correct unit to be "S". However, in the graph the unit is correctly displayed, as shown in the attached fig. Is this a bug?
No, it's not a bug it's a feature, actually. Take a look at the lower left corner in your attached picture. There is some setting called 'Trial Exponent', which is set to six. This means, that the preview shows you 10⁶ X 'your unit' or 'Mega Seconds' in your case. ;)