Seesmic Web has had a problem for as long as I've used it. I was hoping they would fix it on their own but as of the last update (which broke Seesmic Web for awhile) would take care of it. The problem is that tweets or other posts just up and disappear while you're in the middle of reading them. I use Seesmic to scan a days worth of tweets because of its compactness and automatic relatively responsive infinite scroll. But you know there's a problem when all of your timeline from "2 hours ago" to "14 hours ago" is missing.

There. I fixed it.

Install Seesmic Zombie Fix for Chrome (and maybe other browsers)

The problem seems to be that Seesmic periodically culls tweets that it thinks shouldn't be shown, maybe because they're too old and there's not enough space (who knows?). This Chrome-based userscript (it should work with FireFox using greasemonkey, and also natively in Opera) watches for the tweet-snatcher to do its reaping and then saves the zombie tweets before they end up in tweet-purgatory. The "saved" tweets will then show up at the top of your timeline with a pink background on the "ago" time.

Caveats: the "ago" time will no longer be updated automatically, and other javascript-y actions on the tweets will no longer be linked up. So the expand-contract on click no longer works. I worked around this by expanding all undead tweets. But at least you will be able to read tweets from hours ago without having them "rapture" on you.