According to Matt Cutts, the head of the webspam team, people have used 301s to abuse rankings by forwarding a bunch of domains to a new one and thus Google has improved how they handle 301 pages. Let us say you moved to a new domain and 301d all of your pages from old domain to respective pages on the new domain. In this case, Google will eventually phase out the old domain from index and bring the new one in.
What you are saying is rare and if you are worried about it you can let Google know about it via Google Webmaster Forums. They are pretty quick at things like this once it gets someone's attention. There could, however, be the reason that the page eventually removes 301 and then puts it back on. Or it could be that the 301 is not shown to Google Bot.