The engine allows blobs and arrays to be sorted on. Both GROUP BY and ORDER BY on blobs can prepared successfully. All versions (except v2.1) throw a runtime error for GROUP BY due to inability to convert from a blob. ORDER BY [a kind of] works in all versions.
As it produces wrong or undesirable results, cannot be implemented properly due to the sorter restrictions and makes very little sense in practice, I'm going to reject this on the prepare stage.