Why do Twitter following and search break so easily?

A simple test. Create two twitter accounts, A & B. Set A to follow B; B to follow A. Follow a bunch of other users on both accounts to simulate typical account activity. Now start tweeting. Do all of A's tweets show up on B's timeline? Do all of B's tweets show up on A's timeline?

I can tell you from my own experience: most of the time, A does not show on B; and B does not show on A. Googling the problem, it appears other are experiencing the same thing, (followed tweets not showing up) but no real answers on fixing it.

Because this problem appears to be the rule, rather than the exception, one wonders what percentage of followed tweets never show up.

I also note that Twitter's search function frequently errors out with the "tweets are taking a long time to load" message. But then if you do the same search in Google, you find what you're looking for.

These failures seem like such basic functionality problems that I wonder how widespread they are.