Thanks to @grebnek in the following forum thread for bringing attention to this matter. In an effort to reproduce @grebnek's raid level change update issue I noticed that the balance status fails to update in the Web-UI.
https://forum.rockstor.com/t/finally-build-my-own-nas/1811

Steps to reproduce (Rockstor version 3.8-14.07):-

Had a single disk pool with single raid level.

Resize Pool - Add Disk - Yes to change RAID level - selected raid1 from drop down and ticked additional disk - Next

Refreshed Web-UI to find Pools - "rock-pool" - Balances tab to read:
ID=2, Status=started, Start Time=July 23rd 2016, 5:36:39 pm, Percent finished=0, Errors=(blank)

Expected it to reflect a status of "running" and the relevant percentage done.

The command we use to track this progress executed on the command line gave:

btrfs balance status /mnt2/rock-pool/
Balance on '/mnt2/rock-pool/' is running
73 out of about 117 chunks balanced (74 considered),  38% left

Once completed the Web-UI correctly indicates status=finished, Percent finished=100.

Related function fs/btrfs.py balance_status(pool)

Note that this issue differs from #1062 in that this balance was initiated from the Web-UI, not manually from the command line.