Red triangle shows on hud display using UI texture packs

Whenever you apply specific resource packs with UI, an annoying red or yellow triangle will appear on the HUD screen. Additionally, whenever you open your inventory and then move your cursor, the triangle will shift to where your cursor was positioned before you closed inventory,

This issue was present in the beta, was fixed in a later beta, but somehow made its way into the full release. The bug appears to be referencing the item lock textures for the inventory introduced in this update.