With regards to the idiom:
jiě líng hái xū xì líng rén
CC-CEDICT: lit. whoever hung the bell on the tiger's neck must untie it (idiom) / fig. whoever started the trouble should end it
I'm wondering why 系 is pronounced xì and not jì in this idiom. I'm accustomed to hearing jì when fastening things, e.g., 上车请系好安全带, so I would expect 系 to be jì when fastening the bell to the tiger's neck. Moreover, the traditional characters 解鈴還須繫鈴人 uses 繫 which indicates it should be pronounced jì.
Question: Why is 系 pronounced xì (not jì) in the idiom 解铃还须系铃人?