When a skeleton hold a bow at offhand and a random item at mainhand, it's hand will just raise like a random zombie when he didn't find any villagers.
Tested with strays, skeletons, and wither skeletons, and all of them triggers the bug either they are holding an arrow(normal item), a tnt(block) or an axe(melee weapon).
All holding bow either main or off hand will not trigger the bug

Triggering
Summon a skeleton(or stray or wither skeleton)
Make its off hand holds bow, main hand holds any item just not a bow
Turn to survival mode(or adventure) then watch it's hands
Expecting: The mainhand will just hold the bow at offhand
Observed: The mainhand didn't hold the bow at offhand