How to replicate
When crouching with an empty hand, an invisible armor stand spawns in front of the player (to my understanding, this is to register the player's right-click to make drinking rain water possible). If you do this while looking at a nearby lava or fire, the armor stand will catch on fire (as seen in the attached image).

Proposed Solution
Adding armorStand.getAttribute(Attribute.BURNING_TIME).setBaseValue(0); below line 423 in PlayerData.java seems to fix this.