This is expected behavior.
For certain Programmable Units (PU), there are
a very large number of grid types that are needed to make up the full PU.
For example, the IO/XIPHY needs all of the following:
- BUFGCTRL IOB
- PLL_SELECT_SITE RIU_OR
If you selects a particular type, then all of the other types for that PU also need to be selected, otherwise the derived range from snapping would be empty.
This is not always obvious, so only the primary grid types (IOB/RIU_OR) are visible when floorplanning a reconfigurable partition.
If you select IOB/RIU_OR, all of the related types that share the same PU will be selected, and vice versa.