The mother of an 18-year-old man who drowned in a bath at a specialist NHS trust has renewed her calls for the chief executive to resign.
Sara Ryan, whose son Connor Sparrowhawk died in July 2013, said senior staff at Southern Health NHS Foundation Trust had failed to learn from mistakes.
She was speaking after the Care Quality Commission (CQC) told the trust it must make significant improvements to "protect patients who are at risk of harm" and that it had failed to learn from several deaths.
In October, a jury inquest ruled that neglect contributed to the death of Connor, who drowned after an epileptic seizure at Slade House in Headington, Oxfordshire.
The learning disability unit, run by Southern, has since closed its doors.
In December, an independent investigation found Southern Health had failed to probe the deaths of hundreds of people since 2011.
In a statement, the CQC said it has issued a warning notice "requiring the trust to improve its governance arrangements to ensure robust investigation and learning from incidents and deaths, to reduce future risks to patients".
Ms Ryan told the BBC: "We're just astonished they haven't improved - they have again demonstrated a failing leadership - they have repeatedly said they had improved ever since Connor died, and they clearly haven't.
"I'm bewildered the board and the chief executive haven't stood down today. The public don't have any confidence in their ability."
The trust chief executive Katrina Percy has rejected calls for her resignation and said she had been "clear and open" about the work needed to address concerns raised.
In a statement, she said: "I have been very clear and open that we have a lot of work to do to fully address recent concerns raised about the trust.
"Good progress has been made, however we accept that the CQC feels that in some areas we have not acted swiftly enough. My main priority is, and always has been, the safety of our patients. We take the CQC's concerns extremely seriously and have taken a number of further actions.
"I want to reassure our patients and their families that I, and the board, remain completely focused on tackling these concerns as quickly as possible."
CQC inspectors visited the trust in January as part of an inspection and will publish their full report in late April.
Dr Paul Lelliott, CQC deputy chief inspector of hospitals and lead for mental health, added: "We found long-standing risks to patients, arising from the physical environment, that had not been dealt with effectively.
"The trust's internal governance arrangements to learn from serious incidents or investigations were not good enough, meaning that opportunities to minimise further risks to patients were lost.
"It is only now, following our latest inspection, and in response to the warning notice, that the trust has taken action and has identified further action that it will take to improve safety at Kingsley ward, Melbury Lodge and Evenlode in Buckinghamshire."
NHS Improvement said it intends to take further regulatory action at the trust to ensure urgent patient safety improvements are made.
It will put an additional condition in the trust's licence to provide NHS services, which means it could make changes to the management.
Dan Scorer, head of policy at learning disability charity Mencap, said the CQC warning notice states that little has changed since the independent Mazars report was published.
"Families are being left questioning whether the death of their loved one should have been investigated and whether the death might have been avoided," he said.
"Whilst Mazars exposed the failures to investigate deaths at Southern Health, we have known since 2013 that 1,200 people with a learning disability die avoidably in our NHS every year. The lack of urgency to tackle this national scandal is unacceptable."
Luciana Berger, Labour's shadow minister for mental health, said she would raise the issue when Parliament resumes next week, adding: "It is extremely worrying that the trust's leadership has not taken the appropriate action to improve patient safety."
A Department of Health spokeswoman said: "The Mazars report into Southern Health clearly outlined wholly unacceptable failings and work is under way to ensure lessons are learnt both by the trust and across the system as a whole."