There is another underlying point to this discussion. During my early days in ATC, it was mentioned that "whenever a telephone rings in an ATC environment, (especially an operational line), the caller usually has important information that needs recording, so make sure you have a pen and something to write on before answering the call".
This is found to be especially true when answering a call from a single-manned EGPX sector, as the controller may be busy talking to planes.
Sounds like a LACC LCE issue. - Perhaps tape recordings should be examined to identify the 'Band 5 miscreant' and a word had in the appropriate LCE's shell-like.
