The O'Connor house was nominated to the heritage register in April 2000 by its then tenant, who said it was a "creative testament to post war architecture of its day".

The public housing tenant's nomination said the house retained original features, including cupboards, the mantelpiece, door handles and mid-20th century light fittings.

A year ago, the government sold the house to private owners for $1.29 million and photographs from its real estate listing do not show the nominated features.

The Community Services Directorate did not say whether the heritage features had been maintained or were still in place when the house was sold in March 2018.

The directorate said the new owners were aware of the heritage nomination as it was picked up in the conveyancing process as part of the sale.

The house is among a list of places nominated to the ACT heritage register but yet to be considered. A Harry Seidler-designed house in Deakin was placed on the register last year, after being nominated 18 years ago.

The nomination said the O'Connor double brick cottage was "the only known and comparatively intact example of its type" and had rose plantings in the front garden from 1948 and a cottage garden in the backyard.

However, there are no rose plants visible in the front yard. Google street view imagery shows there were no significant rose plantings visible in 2009.

Photographs taken in February 2018 when the house was listed for sale show a bare backyard and incomplete light fittings. The bathroom and kitchen were not in original condition.

A backyard shed, identified in the nomination as being in good condition, is worn and weathered in the photographs.

A spokeswoman for the directorate did not say answer specific questions from The Canberra Times about whether the government had removed the rose garden or when. Nor did she answer questions about what the directorate had done to ensure its nominated heritage values were retained until the Heritage Council came to consider it.

But a spokeswoman said for the ACT government said the heritage status of a public housing property informs whether Housing ACT kept or sold a property.

"Where the registration is particularly restrictive or requires costly maintenance, Housing ACT will generally sell the asset," she said.

The new owners did not comment.

Meanwhile, the owners of several other nominated houses were unaware their properties had been nominated for heritage listing when The Canberra Times called this month.

In one case, the owner of a Forrest home thought the nomination had been withdrawn, while one other owner, who had lived in the Aranda house since it was built in the early-1970s, said while there had been talk of nominating the house, he was not aware it had been nominated.

ACT Heritage Council chair David Flannery said he could not comment on the O'Connor rose garden.

He said the council and its staff worked hard to reduce the nomination list but there was a limit to the number of places that could be assessed in each meeting.

Houses were assessed one at a time because there was a higher risk that their registration would be appealed, which takes staff away from other assessments, he said.

"On the flip side of that, people and groups keep nominating new places, which shows the support given by the community for heritage protection."

Mr Flannery said nominated properties triggered a referral to the council when a development application was lodged, but was unable to comment on the specific property.

An owner or tenant could have modified the garden without a development application.

Mr Flannery said the council considered more than 600 referrals a year and lots of good work was completed by people making additions and alterations to their nominated properties.

"The registration process is not proposing to freeze something in time," he said.

Mr Flannery said the nomination process had changed since 2004, when new heritage legislation was introduced. It now requires a more comprehensive nomination.

He said owners were sent a letter when their houses were nominated and when the process to review the nomination began.

A final notification of the review's outcome was also provided to property owners, he said.

There are 23 private homes nominated to the ACT heritage register among 94 outstanding nominations, which has fallen from 108 in June 2017 and 136 in June 2016.