iOS 9 contains a bug preventing devices with Guided Access on from auto-locking, which could potentially lead to batteries draining and dying for users who rely on the accessibility feature.
The problem manifests regardless of Auto-Lock settings, developer AssistiveWare noted on Facebook. The issue has also been raised on Apple's support forums.
Affected devices will eventually dim their screens, but won't actually go to sleep until someone triggers the Sleep/Wake button. That, however, requires making sure the button is allowed by triple-tapping the Home button to reach Guided Access settings, and could defeat the purpose of the mode.
Guided Access is an option meant primarily for parents, teachers, and others helping those with attention or sensory disabilities. It is also sometimes used as a way of turning an iPad into a makeshift kiosk.
The mode can be used to lock users into a single app, set timelimits, and/or completely disable touchscreen controls. Touch input can also be restricted selectively so that only some portions of the screen will work.
Numerous bugs have been reported since iOS 9's debut on Sept. 16, though most have not been serious and may sometimes be linked to app compatibility. Nevertheless Apple is already at work on iOS 9.1, and could release interim updates if necessary.