Nether vegetation, such as Crimson Roots, Warped Roots, and Nether Sprouts can be set on fire by adjacent lava blocks despite the fact that none of this vegetation is supposed to be flammable.

IMPORTANT:

This bug report does not duplicate MC-170949 as the issue described by that bug report was the fact that fire was not destroying the Nether vegetation. The issue described in this bug report is the fact that the Nether vegetation can be set on fire in the first place.