It seems the most common issue with the comment quoting bug is including @username type references. When it existed in the quoted comment, it broke the new comment. This is now fixed (yes, finally).

For the most part, comment quoting should be solid again. However, there may be other more, less obvious issues with some other special cases, but we don't know what those are. If you come across broken comments submitted after this ST post, please let us know here so we can hopefully get an idea how to fix them.