[Evolution] Meeting invitation responses always Tentative

[Graham Murray <GMurray webwayone co uk>]

Evolution version 3.6.2 

Whenever I receive a meeting invitation (from the exchange server) and
press 'Accept', the sender always sees it as a 'Tentative' response. The
meeting requests give the options of 'Decline', 'Tentative' and
'Accept'. Whether I choose 'Tentative' or 'Accept', it is always
actioned as Tentative.