The unknown signal interference which bedevilled the Circle Line last week has ceased as mysteriously and suddenly as it has started.
The Land Transport Authority (LTA) said trains have been running smoothly since last Friday evening - a change from the unprecedented glitch which affected service for thousands of commuters.
But another problem surfaced at around 8.30pm last night. A track fault caused a 10-minute delay in travel time from Paya Lebar to MacPherson - just one stop away.
SMRT tweeted at 9.15pm that it had been resolved, but was not able to say what the fault was or why it affected only travel between two stops.
On the signalling issue, LTA reiterated a statement on Saturday, that there has been "no loss of signal communication since 4pm on Friday, and service is running normally".
Investigations into the source of the interference are "still ongoing".
SMRT is still manning the fiveyear-old driverless line just in case.
Together with train signalling systems supplier Alstom, SMRT and the LTA found last week that there was a "presence of an interfering signal" in the Circle Line tunnels which was "within the operating frequency band" of the trains' signalling system. But the experts have not been able yet to identify the source or nature of the interference.
Mr Sitoh Yih Pin, chairman of the Government Parliamentary Committee for Transport, said this is "a cause for concern that needs to be fully investigated and rectified".
He added that "we should allow the authorities and SMRT to complete their investigations".
Commuter Alvin Koh, 40, said he was puzzled that the experts were unable to know more about the interference. "I studied electronics and telecommunications, and every type of signal has a certain signature that tells you if it is coming from construction, telecommunication or the military," he said.
Mr Koh, a human resource practitioner and Serangoon resident, said he was stuck in a train last Friday afternoon. He said SMRT has to know the source of the interference to prevent it from recurring.