Report Designer and additional factors

When I want to use an Additional factor from the MES module in the report designer, if the column name is a Delta then the report module doesn’t seem to know how to read the key. I think it is to do with having the delta in brackets in the key name. I’ve got around it by scripting the dataset into another table with a column name without brackets.

This is the key: @BMOil.BM1 Oil Consumption(Delta)@
Results in in the report.

Am I doing something wrong or is this an issue?