Apple is acting erratically when third-party apps make use of its emoji set outside the keyboard, causing confusion among developers over an apparent change in how its rules are enforced. Apple owns the copyright for its emoji, which became a global phenomenon in 2011 when it introduced a dedicated keyboard for them. But until very recently, developers used Apple emoji liberally outside of the keyboard — as decorations inside their apps, and in screenshots and other promotional materials.

Apple has not responded to repeated requests for comment.

WhatsApp and Slack are among the major developers that have changed their emoji in recent weeks in response to pressure, as Emojipedia noted this week. Ryan Nystrom, an engineer at Instagram who is working on a GitHub notification app, tweeted a rejection from Apple indicating that he had violated App Store rule 5.2.5: “Apps and extensions, including third party keyboards and Sticker packs, may not include Apple emoji.” (Nystrom’s tweet was first noticed by Mashable.)

WhatsApp, which introduced its own emoji set in October, declined to comment. Slack introduced its new emoji Tuesday; a spokeswoman would not comment on the reasons behind the change but said, “The style of emoji you see in Slack now varies depending on the operating system of your device. This means, depending on the device, the emoji you see may look different. Apple-style emoji will only be available on iOS/mac devices, while Android, Linux, Windows and Windows Phone devices will view Google’s emoji style.”

While Apple appears to be enforcing rule 5.2.5 more aggressively, it does not seem to be doing so consistently. Developer Sam Eckert said his iOS app had initially been rejected for including Apple emoji, but it yesterday was approved with the emoji still included. He told me today he still doesn’t know what happened.

Whatever the case, developers are on edge. Over the past day, three app makers have told me that the uncertainty around emoji use has roiled their teams. Depending on how widely emoji are used in an app, a change in enforcement could require an extensive — and expensive — redesign. Slack allows users to react to messages with any emoji, for example, and current App Store screenshots show Apple emoji posted underneath messages.

Forcing developers to create or license their own emoji will be a headache that grows every year as more emoji are added. Today the Unicode Consortium approved 157 new emoji for 2018, bringing the total to 2,823.

On one hand, Apple may be acting in the belief that its actions protect its copyright. But on the other, developers I’ve spoken with say they’re frustrated the company hasn’t been more forthcoming. Where and how can developers use Apple emoji? For now, the company isn’t saying.