The Bug
Despite the Bell & Dragon Head being powered by redstone they are not apart of the redstone category they are apart of decorations.
Note
This is probably WAI but other blocks like Note Blocks & TNT don't give off a redstone pulse but are still activated by it and in the redstone category.
Linked issues
Comments 2
From now on, we only accept reports about "incorrect" creative inventory sort ordering if the items/blocks were added in the Nether Update (1.16) or later. All other issues will be closed as a duplicate of MC-1797, which has been marked as Invalid due to the fact it is seen as a feature request.
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Can confirm. Dragon head is already under under decoration grouped with the other heads, so that may be intended, but mojang decides that.