I'm sure many have pointed it, already, but the MAIN bug in here is how the 'Advanced Search' (lol) does NOT work well.
Many times, since 2010, I simply tried searching for my user name, selecting ALL threads..
..and the results are completely varying, and the system does not allow seeing ALL posts ( no "Next" button ).
I find this REALLY bothering, since I like to retrace my activity, to find back my old posts..
..and I COULD do so rather easily with the old system!
I think the problem is that it's only giving back one page worth of results at a time. Even though you may have multiple pages that qualify in the search parameters. The only work-around I can think of at the moment is to subscribe to your threads/posts as they show up in searches. But that would be kinda sucky for people who post a lot.