TAIWAN’S National Palace Museum said it disciplined two staff members who accidentally damaged historical artifacts, after an opposition lawmaker accused it of a cover-up.

The institution – which houses one of the largest Chinese artwork and artifact collections in the world with over 600,000 items – said a member of staff had dropped and broken a 18th century Qing dynasty porcelain plate in May.

The incident, as well as two earlier breakages involving a Ming Dynasty dragon-patterned bowl and a Qing Dynasty yellow bowl, were previously undisclosed. The issue had dominated headlines in Taiwan over the past week after opposition Kuomintang lawmaker Charles Chen received a tip-off of the incidents and accused the museum of a cover-up.

The museum said in a statement Thursday that one member of staff was given a demerit due to negligence, while another was issued reprimands. It denied earlier that there was a cover-up, and said that the items will be restored.

Most of the National Palace Museum’s major pieces such as jade and bronze works came from China’s imperial art collection, brought to Taiwan by Chiang Kai-shek’s Nationalists.

A museum spokesperson declined to comment on the value of the damaged items. Museum director Wu Mi-cha told reporters last week that their value was “far lower than” the NT$2.5 billion ($78 million) mentioned in media reports.

Other major museums have had similar problems. In 2011, damage to a Sung dynasty dish at Beijing’s Palace Museum came to light on social media, leading authorities to set rules about reporting damages to first-tier national treasures. The British Museum admitted in 1999 to covering up damage to the Elgin Marbles from Greece after a botched cleaning effort in the 1930s.