Short answer
I've created a pull request with a fix for Ami's branch:
https://github.com/amiyasahu/Donut/pull/145
Long answer
When I was pushing updates to the OSN plugin, I failed to realize that nav_user_search() was not a CORE extended function, but a SnowFlat theme defined one instead.
So there's many places in themes, and plugins where I updated code to point to that function. But since this wasn't a CORE defined function, the changes failed to automatically fold into place, for this case.
When I was creating the pull request above, I pondered about reverting back to the way the Bell was being outputted, using doctype() , but even though that worked in most of my themes without changing any code, it did not work for SnowFlat theme. Which is the most important theme, since it's the default Q2A theme and many custom themes have branched from it.
I also didn't want to use Javascript to manipulate its output location, after rendered.
The Solution
So the wiser solution was to create an empty nav_user_search() function for the Donut theme, and append its output next to the User Navigation Avatar, since most of the themes (derived from SnowFlat) already have this function.
I could have created a pull request to the CORE with this function, so this issue would solve itself for other theme developers, but I believe this will be the faster solution for now.