I just ran into this myself. It’s… extremely annoying. Any update, is there a way to change this now? “About” really should not be a filtered word for search! Here’s how I ran into it here on Meta:
I was in the Plugins category and noticed that some plugin topics auto-delete replies, and others don’t. So I went to see if there was an explanation for this in the About topic in that category. There wasn’t, so I was going to ask about it, but wanted to make a feature request to a plugin first (in an auto-deleting-reply topic 
). So I went back to the main category list and made my reply. Then I went back again to the category list and tried to find The About the Plugin category topic. Since it was an older but pinned topic, and I had already read it… it was no longer visible in the list (it had been moved down to its date-appropriate position now). 
OK, no problem, I’ll just Search for it… But of course, no dice.
The bigger issue is that there is absolutely no in-UI warning or message about this. The search just silently fails. So if this is unfixable due to Postgres limitations, I’d like to strongly suggest you add a feature into Discourse that notifies people of these words being filtered from search! Otherwise it’s quite confusing.