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.
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.
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