Here is the response I got from the Composite WPF thread:
We have been looking to reproduce your issue and you are right, this does happen. Having done some digging, we have not been able to determine the root cause yet, but we can tell you our believes
based on our findings:
DataGrid appears to calculate its size once. Then, when the UI is updated, say you resize the window, it uses that previously established size to assign the new width/height to the columns and rows.
It appears that when loading the grid (placed in a view) into a region in the module initialize of your modules, the size that it will get is not yet determined, thus it
miscalculates the width it should get. This makes the column assigned with the “*” width appear wider that it should.
Add the GridView to the region after the application has been loaded. (tested)
Load the module that has the grid on demand after the application has been loaded. (tested)
Check how to update the WPF GridView’s code to calculate the size of the Grid so it has the real size of the view.
Please let me know if this helps.