[Code Folding] opening of collapsed anonymous class doesn't work

[Wittmaxi]

Description
I cannot open a collapsed anonymous class after collapsing all. Works fine with methods.
The "+"-icon that indicates code folding correctly changes to "-"

Copy of eclipse-platform/eclipse.platform.ui#1182
Reproduce
In a File with anonymous classes, use "Folding -> Collapse All". Try to uncollapse the anonymous class

Expected behaviour
I expect the anonymous class to unfold like any other folded block.

My system
Eclipse SDK

Version: 2023-12 (4.30)
Build id: I20230913-1800