Because of the complexity of the column pinning and multiple row header features and the styling requirements of each of them, it's not feasible to make both of these features work together. More specifically, the column pinning feature is based on adding some dynamic CSS to re-position all the cells of a column, plus header and footer, at the left of the table, without having to add additional nodes. In the case of multiple row headers, parent header cells in the top rows can have a variable column span, so it would result in various types of conflicts trying to move those header cells to the left, especially when other unpinned leaf header cells have those same parents cells above them. There would be many possible cases and scenarios to cover, that it would require some considerable effort and time to make this work perfectly. Most likely, in order to support these features together, we would have to completely change the current tried and tested approach to column pinning to something more complex that would involve creating nodes dynamically.
Improvement
Major
ICE-8888
ace:dataTable, issue with column pinning when using filtering
Because of the complexity of the column pinning and multiple row header features and the styling requirements of each of them, it's not feasible to make both of these features work together. More specifically, the column pinning feature is based on adding some dynamic CSS to re-position all the cells of a column, plus header and footer, at the left of the table, without having to add additional nodes. In the case of multiple row headers, parent header cells in the top rows can have a variable column span, so it would result in various types of conflicts trying to move those header cells to the left, especially when other unpinned leaf header cells have those same parents cells above them. There would be many possible cases and scenarios to cover, that it would require some considerable effort and time to make this work perfectly. Most likely, in order to support these features together, we would have to completely change the current tried and tested approach to column pinning to something more complex that would involve creating nodes dynamically.