Bench rebuild-global-search doesn't work ok

I may have missed something but…
I have set DocType->Purchase Receipt Item → Item Name “In Global Search” checkbox and also put a checkbox under “Make “name” searchable in Global Search” (by the way - what’s the difference between those?)
When I create new Purchase Receipts the DB field “content” fills with purchase receipt item names which is what I want.
But if I want to update older entries by running “bench rebuild-global-search” all those purchase receipt item names disappear from the content column even in new entries.
Am I missing something or is this a bug? Version is 12.
Thanks and regards,