Duplicate texture files for the side and top of the Warped Stem are present in the assets/minecraft/textures/block/ folder.
The files used in the block model are:
stripped_warped_stem.png
stripped_warped_stem_top.png

The duplicate files, that are not used nor follow the normal naming scheme are:
warped_stripped_log_side.png
warped_stripped_log_top.png

As far as I can tell, the pairs of textures are identical.