The Mossy Vines and Sea Strider Dens have no effect while smoldering, which means they may start burn without the player knowing they were smoldering in the first place.
1. Place a burnable item under a mossy vine and/or sea strider den
2. Burn the item
3. Notice the mossy vine and/or sea strider den smolders indicated by the name change e.g. "Extinguish Smoldering Mossy Vine" but the smoldering effect does not show
4. be sad because your mossy vine now burnt : (