Adrianus Van Ham, 44, drowned in the incident at South Hook liquefied natural gas (LNG) after getting trapped inside a cabin by his life jacket.
The BBC reported that the inquest at Haverfordwest heard one of the legs of the platform at Milford Haven had risen too high from the seabed.
A safety inspector said they had found no mechanical fault.
The men in charge of the platform said there were problems with its stability.
They had also had problems with the controls, the hearing was told.
Barge master Archie Keenan and his assistant John Smith had already said there were problems because of the platform's size - it was very small, yet carried a huge crane.
ADVERTISEMENTA Health and Safety Executive inspector told the inquest they had not found any mechanical fault with the platform.
But the inspector admitted the controls had not worked satisfactorily that day.
Mr Van Ham, a trainee barge master, was killed on 6 October 2007 when he became trapped in the submerged control cabin by his self-inflating life jacket.
The jury had to choose whether he died by accident or misadventure
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