Toilets on a fleet of state-of-the-art trains are being re-fitted because of damage caused by high speeds.
Passengers like the train but not its toilets
Plumbing on Pendolino tilting trains has been affected by vibration as they travel at speeds of up to 125mph.
Virgin Trains, which operates the Pendolinos, said leaks had led to customer complaints.
But reports it is to replace automatic doors after passengers complained they could open while the toilet was in use were "absolute rubbish," the firm said.
Technicians have been called out to deal with customers trapped inside toilets with conventionally operated doors after bolts had become stuck, the firm said.
But it denied reports in the Daily Telegraph about automatic doors opening unexpectedly or locking people in.
Problems with disabled toilets on the hi-tech tilting trains however were down to people not using the automatic doors properly, a spokesman said.
"There's a button to close the door and another with a key symbol on it which locks the door and flashes when the door closes," said David Ewart, communications manager with Virgin.
"It's pretty clear what you have to do. We've even got signs in Braille," he added.
Rail watchdog group Passenger Focus, however, said there might be a need for Virgin to have clearer instructions for customers.
And the new plumbing may help with a problem raised regularly by travellers, according to the watchdog.
A spokeswoman said: "Having clean and pleasant toilets available hasn't always been the case on Pendolinos and passengers have flagged this up to us."
The watchdog's annual survey of 1,500 passengers using the line between London and Glasgow found 52% were satisfied with the state of the toilets - below the average for passengers on all Britain's train companies.
Virgin admits passengers have complained about onboard smells from the toilet system.
"We have got a programme underway to re-design the toilet pipe work," said David Ewart.
Problems follow a ban on old style toilets that flushed onto tracks
"It has been shown to develop leakages because of vibration at high speed and the work is intended to make it more robust."
Industry experts say the airline-style toilets on the Pendolinos, which in order to meet new health and safety guidelines store waste on board rather than flushing it straight onto the tracks, are also prone to blockages.
"People just ignore the warnings about what they can flush," explained Chris Milner, deputy editor of The Railway Magazine.