An XMLStreamReader component should always leave the reader in a predicable state.
For every other AttributeParser implementation:
Prior to calling AttributeParser.parseElement(...), XMLStreamReader.getEventType() == XMLStreamConstants.START_ELEMENT
After calling AttributeParser.parseElement(...), XMLStreamReader.getEventType() == XMLStreamConstants.END_ELEMENT.

AttributeParsers.MapParser complies with the above entry and exit criteria when configured with an element wrapper. However, when configured without an element wrapper, this method leave the reader in a different state: XMLStreamReader.getEventType() == XMLStreamConstants.START_ELEMENT.

The parser introduced via WFCORE-6779 validates the above entry/exit criteria, and naturally fails when using AttributeParsers.MapParser without a wrapper element.