Cave vines cannot be placed on the underside of leaves.
This makes sense for blocks such as bells, however leaves can support normal vines, so it'd be expected they they'd also support cave vines (and possibly other blocks such as weeping vines) by extension. This, however, does not happen.
Right click with vines on the underside of a leaves block, and do the same with glow berries.
Both of these place a type of vines, so it'd be expected both would be supported by leaves.
Normal vines are placed just fine, but cave vines completely refuse to be placed.
It may be worth adding a tag of some sort, perhaps #minecraft:vine_support_override, which itself contains #minecraft:leaves. This tag would allow any block in it to support all types of vines (vines, weeping, twisting, cave), regardless of any other factors like its solidity or support shape.