Why are hashtagged tweets no longer showing up?

[nickmasta]

A bunch of people at my school have been hashtagging one of my teachers on twitter. He is cool with it, but only like 3 tweets show up when you search the hastag, and after a while they dissappear and a couple new ones show up. I tried clicking the button to view less important tweets, but that doesn't do anything. I know I can view other students' tweets because I have seen them when searching the hastag before.

[KirstyTMB]

Maybe they have deleted their tweets which would mean you cant see them. other than that, if you say you are clicking to view all not just the top tweets then im not sure. maybe a fault with twitter, that has happened before.