An example:

import std.stdio;
struct S
{
   int i;
   ~this() { i = -1;}
}

void main()
{
   int delegate() dg;
   {
      S s;
      dg = () { return s.i; };
      writeln(dg()); // 0
   }
   writeln(dg()); // -1
}

Allowing access to a destroyed variable where a destructor has invalidated the object should not be allowed. Prior to 2.053, this was an error. According to Paul Backus, the responsible PR was this: https://github.com/dlang/dmd/pull/5292

One who has created a delegate would probably expect that when calling the delegate at a later time, the state of the object should be preserved, and not destroyed. For some cases, it might be dangerous safety-wise to use an object after destruction.

Fixing this issue probably requires a long deprecation period, as no doubt code that depends on this (or works in spite of the dangers) exists today.