After talking with a few people i have reached a different conclusion that this may be more about pure stylistic influences and nothing more.
Beginning in the 1700`s European culture and style began to influence Javanese style and culture. European clothes and dress styles were adopted by the Javanese upper class and elites. You can see a good illustration of this in a mid-19th century lithograph reprinted in van Duuren's "The Kris" on page 60 which depicts a Madurese prince wearing a European military jacket and tri-corner hat a part of his royal dress.
Weapons were no exception to this influence from the West. The typical European scabbard for a sword, as seen by the Javanese, had a metal chape and locket, with the central part of the scabbard smooth wood, or wood covered with leather. The Javanese copied European blade styles, and European scabbards, and many examples of Javanese swords can be found where the sword is a direct copy of a European sword, or is a mix of both European and Javanese styles, perhaps with a Javanese style blade housed in a European style scabbard.
Later, when Javanese scabbards began to be made of metal, the appearance of the old style scabbard with metal chape and locket, and smooth central section, was imitated.
So there is one other explanation you can add to the possible reasons for these motifs.
