cc @IljaN @cdamken
In the old logic might break when a group share has been mounted by multiple users and files are repeatedly moved in and out of that group share while encryption is enabled.

• Needs a Unit test that reproduces this bug
  • enable encryption
  • create group share, accept it for multiple users
  • might depend on order of acceptance (which is the order read from db)
  • has to do with additional user filesystem initializations in

    core/lib/private/Encryption/Keys/Storage.php

    Line 386 in 78fcc9e

    \OC\Files\Filesystem::initMountPoints($uid);

    , called by

    core/lib/private/Encryption/Keys/Storage.php

    Line 344 in 78fcc9e

    $this->setupUserMounts($owner);

    , called by

    core/lib/private/Encryption/Keys/Storage.php

    Lines 319 to 320 in 78fcc9e

    	$sourcePath = $this->getPathToKeys($source);
    	$targetPath = $this->getPathToKeys($target);

    (which initializes source & target), called by

    core/lib/private/Files/Storage/Wrapper/Encryption.php

    Line 783 in d329971

    $this->copyKeys($source, $target);