WordPress 7.1 removed the core check that kept classic editors and ACF blocks un-iframed

What broke

An upgrade to WordPress 7.1 left a client site with a broken editing experience, according to a post by Max Soskind on dev.to. Custom blocks built with Advanced Custom Fields (ACF) suddenly moved their field controls off the canvas and into the sidebar, and on one site the blocks stopped saving entirely — with no error shown to the user. Soskind's diagnosis: the problem is not in ACF but in a change to the block editor's core JavaScript.

The behavior that disappeared

Through the 7.0.x series, Soskind explains, the editor only wrapped the post canvas in an iframe when every block in the post declared block API version 3 or higher. ACF blocks default to block API v2, so a single ACF block anywhere in a post was enough to keep the entire canvas un-iframed. Sites running classic-editor-style workflows and inline field editing depended on that behavior, often without knowing the dependency existed.

In 7.1 the gate is gone. The author reports that the identifier disableIframe no longer appears in any file under wp-includes/js/dist/, and that editor.js now passes shouldIframe: true as a hard-coded value. The practical effect is that the canvas is always iframed, no matter which block API versions the post contains.

A ten-second diagnostic

To check an install directly, the post suggests one command:

grep -rl "disableIframe" wp-includes/js/dist/

Soskind's rule of thumb: four matching files means the site is on 7.0.x and the old gating logic is intact; zero matches means the check has been removed and ACF field placement will move. Because the breakage is silent — the affected site produced no save error at all — checking the installed core files this way can be faster than debugging through the editor interface.

Why updating ACF does not help

Soskind is explicit that updating ACF will not restore the old workflow. ACF's v3 blocks, he writes, adopt the new editing model rather than restoring inline editing, so a plugin update swaps the broken behavior for a different one instead of returning the un-iframed canvas. The post points to a longer post-mortem covering the core diff and a fix, but the dev.to summary does not detail the remedy itself.

Why it matters

The breakage pattern matters beyond this one upgrade. An implicit, undocumented behavior of the editor internals — iframe gating tied to block API versions — disappeared in a version bump, and the resulting failures surface in confusing ways: field panels relocating to the sidebar, and saves that quietly do nothing. For agencies maintaining long-lived client builds, the lesson is that the compiled editor bundles under wp-includes/js/dist/ are not a stable contract. The grep above doubles as a cheap pre-flight check: run it after a WordPress update, and if the match count changes, regression-test ACF editing and saving on a staging copy before touching production.