When the Choi Hung was first built in 1979, it only had two rain tracks just like the rest of the stations at the time; along with the penchant for trouble.
Before being open to the public, it was mandatory to conduct test runs from Choi Hung station to Kowloon Bay station, which would normally take 3-4 minutes.
Being as everything worked smoothly, the staff couldn't understand why the ride took unusually long 30 minutes. Upon their return, staff that participated in the test run was found in a delirious and overwhelmingly spooked state.
When the test run was conducted for the second time, spooky results persisted.
It was later determined, with Geomancer's help, that the train tracks ran straight through what is considered to be the Gates to Hell itself. 
As a result, MTR decided to build another track next to this one, to avoid sending their customers to Hell by accident...