I seem to have found a bug with the .isl files. My issue is that I have an MDI tab application in which one screen updates the state of a handful of controls on another screen. For example, it may change a textbox from ReadOnly to enabled.
I noticed that when I then go back to the other tab that contains the controls with the updated states, I must "hover" over the control for it to "re-paint" itself with the correct style.
This is a strange one...but I have verified that it does not happen when I do not load an .isl file.
There was a bug in the grid similar to what you are describing that was recently fixed. So I recommend getting the latest Hot Fix if you do not already have it.
If that doesn't help, you should Submit an incident to Infragistics Developer Support
For more clarification, this seems to happen when I am using the Default Office 2007 Blue isl file. In addition to the above I have also noticed that when using this styleset with grids, the cell text disappears when clicking around the grid. Then when a cell is hovered over, the text reappears.
So this might be a specific problem with the Office 2007 Blue styleset.