Update to latest upstream version, see following page for changes:
https://www.mozilla.org/en-US/thunderbird/38.1.0/releasenotes/
This update also should fixed problems with thunderbird-lightning-gdata package.
Rebase to Thunderbird 38. By this release thunderbird-lightning (calendar) package has become obsolete, because it is a part of Thunderbird 38 package now.
For changes see: https://www.mozilla.org/en-US/thunderbird/38.0.1/releasenotes/