When mob head is held it appears smaller than heavy core which is as big as creeper head when placed.It is also held closer to right than other blocks and items.
How to spot the offset :
1.put heavy core and any head/skull in your hotbar
2.select hotbar slot with heavy core
3.select hotbar slot with head
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Thank you for your report!
We're tracking this issue in MCPE-141365, so this ticket is being resolved and linked as a duplicate.
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