Multilevel BOM does not display exploded Items list at top level

A top-level BOM in a multi-level BOM hierarchy will not display the exploded view of Items in either the “BOM Explorer” or “Browse BOM” view. Only the single Item contained in the BOM is shown.

Duplicating that BOM does then display the exploded view correctly for the duplicate BOM.

The only difference I can find between the original and duplicate is that the original is referenced by a Production Plan - so the BOM can’t be Cancelled.

Any suggestions as to what could be preventing the exploded view showing for the original BOM for this top-level Item? Is it because of it being referenced in the Production Plan?