Synology have released an update to their NAS software, with several important fixes.
Version:5.2-5592 Update 2
1. Fixed an issue where DS1515 would be unable to shut down properly.
2. Enhanced RAID reliability when repairing volumes from degraded state.
3. Improved the stability of LUN backup.
4. Improved memory usage for Btrfs file system.
5. Improved the compatibility with UPS devices.
6. Improved the stability when repairing the passive server of a high-availability cluster.
If you haven’t upgraded to DSM 5.2-5592, it can be found here – http://www.synology.com/en-global/support/download