It looks to me like the letter spacing is being automatically adjusted when using Group Headers. You can see it visually in this screenshot on the "Test2" line:


Here are the values for each row header:

"Test1: $666.00   (Tax Rate: 8.75%) Hardware Markup"
"Test2:                                         $393.00"
"Test3: $1,019.00   (Tax Rate: 8.75%) Hardware Markup"

I have made this example extreme on purpose to illustrate the issue. I added a lot of spaces between "Test2" and the number, but I did not expect it to stretch the font out like this.

See how (for example) the $393.00 looks like i have it set to $ 3 9 3 . 0 0?

I have read about CreateRowCellStyleDynamically and GroupRowLevelStyles but I cannot figure out what I need to do to prevent this.

This is probably going to be really easy for you to answer, hopefully.
iGrid uses the standard Graphics.DrawString() method to output cell texts. Sometimes this method works strangely, and it seems, what you discovered is one of the cases. At least, we do nothing in iGrid to spread text in group rows and occupy the whole available viewport width.

The only idea that came into my mind is to try to experiment with the flags in the TextTrimming and TextFormatFlags properties of the corresponding row text cells. Perhaps, this odd behavior can be 'turned off' if you enable or disable some features controlled with these properties.

Keep us informed, please.
I seem to have found a way to fix it, now knowing that it had nothing to do with anything you were doing to it in the control.

I cannot explain why this fixed it, but your hint that it was using the standard Graphics.DrawString() method helped me know what to play with.

The grid defaults to the system font I guess, which has a size of 8.25 - All i did was change the size to 8.5 and it no longer had the problem.

IGrid1.Font = New Font(IGrid1.Font.FontFamily, 8.5)

Edit: Well, that worked in my testing application, but not when I added it to my main project, so I will continue to keep you updated if I learn of anything else.