The bug can best be described as the following:
When setting a radgrid datasource with an IEnumerable, filterexpressions behave not as expected.
Create a radgrid with EnableLinqexpressions set to true, and set its datasource to an IEnumerable. Set a filter on a column. Check the filterexpression that is being generated. Notice the filterexpressions is NOT a valid linqexpression, but has the following format: "([CustomerID] LIKE '%ALFKI%')";
Now set the datasource to a list instead of an IEnumerable. Notice that suddenly the filterexpressions that is generated is different.
See also your Filterexpression documentation
I have a requirement where i have to set an initial filter in a grid when opening the page. But we also have export buttons on that page that use the grids filterexpression to filter a dataset for the export. This no longer worked because the filterexpression was no longer a valid linq expression. In my opinion this behavior is not very intuitive, and i could not find any documentation about it.