@GoZ: See these lines:
Here inside str_replace we are searching for the "&amp...

@GoZ: See these lines:

Here inside str_replace we are searching for the "&" and replacing it with which works well if string does not contain any encoded html entities. Like you tested. But this is not the case to reproduce this bug. Use a string contains already encoded html entities. like the following string:

The str_replace output will look like this:

Not sure rest of the code takes care of this situation.