The 10-10 patch added input buffering for abilities, but it doesn't seem to work for active items cast during Haze ult's windup. This repros in Sandbox, and I tried with Vampiric Burst and Ethereal Shift as well. I tried some other abilities that I expected would have similar lockouts (Mo Burrow, Viscous Goo Ball) and the item casts weren't even delayed until the windup finished.
"- Haze: Bullet Dance now allows you to use items during it" from the patch notes does not really state what you are projecting in your reply.
It could clearly be a bug. Might also not be, but we would need confirmation from the devs.
It also seems like an arbitrary distinction to have input buffering for abilities, but not for items used during the windup of one particular ability. Inconsistencies like that are usually unintentional unless there's a clear reason.