IVAN - I have no problem sitting down with a musician and being accompanied (by prior agreement).Songs written to be performed that way sound better that way!Harmonies can be wonderful and I have enjoyed harmonies added by the audience. Indeed many songs are dramatically enhanced by added harmonies.
There has not been a problem as yet with musicians joining in with me uninvited probably because most of the places I sing in accept solo song as valid in its own right. This to me is the real issue.
Happy singing to you all. John