As you say
I know that if they type a value OVER the zero ETC, it creates a PENDING ETC
but on the timesheet that displays as ETC. It should also display as ETC in Clarity while pending ETC displays as proposed ETC.
The only way I am aware of to solve that is to either accept or reject the pending ETC.
I have not tried if changing the ETC to something else in OWB or Clarity, saving and the setting the ETC back again will change what is displayed on the timesheet.
The other option is to just ignore it. You know the PM's are expected to communicate regularly with their team members on matters like this.