In editorial appeals findings published today, the committee said that the shorter headline "David Cameron attack on Welsh NHS" was linked back to a story on the BBC News website headlined "David Cameron attacks Labour's handling of NHS Wales".
The shorter headline is produced for the website index and is also "fed through to Ceefax (being phased out), Twitter and elsewhere, and was designed to fit all of these other platforms", the committee report explains.
A complainant had argued that the headline, which he saw via Twitter, was inaccurate "because it suggested an attack on the NHS in Wales, whereas the object of the attack, as described in the full story, was the Labour Party's handling of the NHS in Wales".
The BBC had responded that it felt the shorter headline did match the story, and that "Mr Cameron had attacked the running of the Welsh NHS, which was administered by Labour."
The BBC also argued that the story "had quoted performance statistics for the NHS in Wales and contrasted them adversely with the NHS in England".
"The BBC said that because the NHS in Wales was administered by Labour it was fair to say that Mr Cameron had attacked the Welsh NHS."
The complaint was taken to the editorial complaints unit but the complaints director decided in March not to uphold it. He was said to have "accepted that the report linked to the Twitter headline was about Mr Cameron criticising Labour's running of the NHS in Wales rather than the NHS", but also "believed that readers of the headline would have correctly understood that Mr Cameron was criticising an aspect (or aspects) of the Welsh NHS, even if they did not know what it was he was criticising without clicking on the link".
The complaints director also "did not accept that those who only read the headline would have been left with a materially misleading impression", the editorial standards committee outlined in its report today.
"It was generally understood that headlines provided a brief summary and readers who wanted more detail could reasonably be expected to click on the link to the full report."
But following an appeal to the BBC Trust, its editorial standards committee upheld the complaint.
"The BBC's view was not accepted by the committee, and it agreed with the complainant that to say the prime minister had attacked the NHS was a very different matter from saying he had attacked Labour's performance in relation to the NHS, particularly given the fact that protection of the NHS was a politically sensitive issue."
The committee's findings also stress the issue of accuracy when dealing with limited space to publish a headline, such as on some digital platforms.
But the committee said "the editorial guidelines on accuracy apply to all content wherever and however it is received".
"It was particularly important for this to be borne in mind by the BBC as it continued in the development of new platforms for delivering its content.
"The committee agreed with the BBC that considerable skill was needed to ensure that headlines subject to space restrictions remained duly accurate. On this occasion, the committee decided, the short headline that was the subject of the complaint was not sufficiently precise. It agreed with the complainant that this meant the headline did not reflect with due accuracy the story to which it was linked.
"In view of this, the committee required that the headline be removed or adjusted in the archive, on the website and on other platforms as necessary."
Update: This article was updated to clarify that the short headline is produced for the website homepage index, which is then pushed out to other platforms such as Twitter and Ceefax.