Did you know there’s one emoji that iPhone users in China can’t see?

The emoji for Taiwan’s flag 🇹🇼, introduced in iOS 9 in 2015, can’t be found on the keyboard in Apple devices where the location is set to China.

If these users receive a text message with the Taiwan flag emoji, they see a white box with an X instead.

The emoji keyboard and Taiwan flag emoji as seen in two iPhones, one with region set to Hong Kong (left) and another to China (right).

This isn’t actually new. It’s been happening for years now. But it gained wider attention this week when cybersecurity researcher Patrick Wardle says he found a bug in this censorship feature that could cause iMessage, Facebook Messenger, WhatsApp and others to crash on some iPhones.

Wardle stumbled upon the discovery when a friend from Taiwan told him that whenever she got a message with the Taiwan flag emoji, or typed the word “Taiwan” -- the app would crash immediately.

Turns out, it was triggered by a bug that struck when the phone had certain language and country settings that included China or Chinese, causing the phone to get confused about what region it’s in.

Wardle’s friend, for instance, had her country set to United States and language set to English, followed by Chinese. The problem was fixed by changing the region from US to China, then back to US.

Wardle later reported the flaw to Apple, which was patched in iOS 11.4.1.

Emoji are part of a global standard, so no matter which country you’re in or what device you’re using, it’s meant to display the same sort of symbol (though sometimes the differences in how they’re drawn can lead to odd results, like the cookie emoji (🍪) appearing as a biscuit on some Samsung devices).

But it’s also not the only case of emoji not appearing on some platforms. Emojipedia notes that Samsung briefly removed a couple of Japanese emoji, like the map of Japan (🗾) and the yen chart (💹), and once changed the crossed flags emoji (🎌) from a pair of Japanese flags to a pair of South Korean flags.

(Emoji originated in Japan, which is why there are so many symbols from that country… and probably explains why, in a country obsessed with trains, we have at least 13 railway-related emoji: 🛤 🚂 🚃 🚄 🚅 🚆 🚇 🚈 🚉 🚊 🚝 🚞 🚋)

In this case, it’s part of a much wider trend. Taiwan is a contentious issue for the Chinese government, which considers the island a breakaway province.

Recently, Beijing has asked three dozen foreign airlines to refer to Taiwan as Chinese territory on their websites.

Failure to comply might have consequences. Back in January, hotel chain Marriott saw its website and app blocked in China for a week after a customer survey listed Taiwan, Tibet, Hong Kong and Macau as separate countries.