I can confirm the bug in 188.8.131.522.
To demonstrate the problem, go to 'Set Ring Tones/Alerts' and edit any ring tone. Quickly scroll through the list and listen to a number of ring tones. At some point in this process, the tones will go silent. The result will be no ring tones or alerts until a reboot.
I believe that there are certain conditions during normal operation that will trigger this bug.
Rather than risk all alerts going dead at unpredictable times, I have downgraded to .681, which seems to be free of this bug.