On the subject of bugs, I've noticed opening Synaptic starts using a lot of CPU "nice" usage for xapian index re-building itself. Not sure why. 
As mentioned by @pfeiffep, the Boutique does have Synaptic under More Software . It also states the "Can't find what you're looking for" in the last paragraph on the first page that appears that advises where more software can be acquired. 
The Software Boutique does have a search function (in the latest update opt-in) but only for the software within the Boutique. This isn't designed as a replacement software centre / package manager.
Instead, it's supposed to be easy for new users who just want the "best" variety of programs that work well in Ubuntu MATE. Originally there was Ubuntu Software Center, but I'm sure a lot will agree it was quite a hog, slow and lacked most desired stuff like Steam, Google Chrome, Skype without having to enable things tucked away in other areas.
I mentioned in your other thread that 16.10 may introduce the ability to search packages in the archives, kind of like Synaptic but much simpler. This isn't a guaranteed feature, just an idea.