In its effort to align with Chinese government content restrictions, LinkedIn has accidentally censored Hong Kong users’ mentions of the 1989 Tiananmen Square massacre, The Daily Beast has learned.

It was a surprise for Andrew Work, CEO of burgeoning Hong Kong political newspaper Harbor Times, when he tried to post a column reflecting on the relevance of the June 4, 1989 events on the social networking site.

Hong Kong, a former British colony, functions as a Special Administrative Region of China, with a separate political system, an independent judiciary, and much broader civil liberties. Unlike in China, discussion of the Tiananmen protests is freely permitted. In fact, the only museum in the world dedicated to commemorating the protests is located in Hong Kong.

Work’s post was blocked and he received the following message:

“LinkedIn determined that recent public activity you posted (such as comments, items shared with your network, or activity in groups) contained content prohibited in China. As a result, this content will not be seen by LinkedIn members.”

It’s a particularly sensitive time for the Chinese government, which has sought to erase from public memory any mention or commemoration of the event that left at least hundreds of pro-democracy activists dead. Reports from China indicate that the government had detained a substantial number of activists in the months leading up to the 25th anniversary on Wednesday of the quelling of protests.

LinkedIn acknowledged that it had blocked the content but said it only affected “a very small handful of our members in Hong Kong. While some of their content may be inaccessible in China, it is accessible elsewhere in the world.”

LinkedIn does typically make a distinction between Hong Kong and China. Usually, content from outside China that the Chinese government doesn’t approve will be censored only for Chinese users. Meanwhile, content posted from within China that does not conform to government censorship will be blocked for everyone, both in China and across the globe.

In other words, LinkedIn meant to treat Work’s post as the former but instead treated it as the latter, as if it was from within China.

The accidental censorship of apparently small amounts of Hong Kong content illustrates the trade-off that American companies, such as the Mountain View, Calif.-based LinkedIn, must make to operate in China.

LinkedIn maintains no servers in China but provides services to some 5 million Chinese professionals in the country. In February, the social networking service launched a local-language Chinese site.

“We’ve long recognized that offering a localized version of LinkedIn in China would likely mean adherence to censorship requirements of the Chinese government on Internet platforms. These requirements have just recently gone into effect,” a LinkedIn spokesman said in a statement. “As we said at the time of our launch in February, it’s clear to us that in order to create value for our members in China and around the world, we will need to implement the Chinese government’s restrictions on content, when and to the extent required.”

To be sure, the trade-off for adhering to Chinese restrictions is a lucrative market of professionals. The company has said in the past that China has some 140 million professionals, making up one-fifth of the world’s knowledge workers.

LinkedIn would not address which issues the Chinese government had asked them to censor content, or the extent to which it had pushed back on these requests.

UPDATE: LinkedIn says that while they sent a mistaken notification advising a small number of users in Hong Kong that their Tiananmen Square content was blocked, they did not actually block content outside of China. According to the social-networking site, their filtering system worked as it was supposed to—blocking Tiananmen content in China, but allowing it in Hong Kong and the rest of the world. This distinction between mistakenly notifying users of blocked content and actually blocking content was not made to The Daily Beast on Tuesday.