I do have a table with different kind of value columns (Int, Double, Long). If I do choose the Type Based Aggregation method in the GroupBy Node, and just want to group by the Data type Long (Sum), the output table also shows Integer columns.
This was already the case in version 3.5, and still persists in 3.7.1.
Let me know if you need any further info - I have attached a small workflow to reproduce the bug.
I have check it and actually this is not a bug rather a intended behavior. If you check node description it says following:
The "Type Based Aggregation" tab allows to select an aggregation method for all columns that are compatible with the selected data type. For example to apply an operation on all numeric columns simply select DoubleCell. This will include all numeric cells that are compatible with DoubleCell such as IntCell and LongCell.
If you only need Long columns in GroupBy node use Column Filter node before grouping with option Type Selection and exlude Int columns
