eject_mount_do() function creates new task to notify caller when asynchronous mount operation is finished. Task has two attached sources: 
(1) error_channel_source which tracks error pipe of spawned mount command
(2) command pid watch source. Both sources has references to task. 
So there are 3 references to task.

When mount command is finished and eject_mount_cb() is called then two of references are released:
(1) by g_object_unref(task) call;
(2) when child_watch source is destroyed from context.

Error channel source reference is not released so: 
(1) task is not released;
(2) eject_mount_op_free() callback is not called;
(3) error stream pipe is not closed.

On my machine it also leads to high CPU usage.