I guess the Javanese culture in Indonesia and Malaysia has differred tremendously, although more or less I can still understand Javanese - pasar & halus
A Malaysian Javanese wiseman once told me not to keep my keris in the casing / ploncon because
"HE" would be "sumbeg" or suffocating, thus advised me to hang it on the wall tip down using a blawong / display board.
The casing / ploncon is usually used to cover up tumbak or spear heads, and when in use for keris, it's when we carry the keris to Upacara Suro or other ceremonies (except the one on your waist).