Eric's recent post about strange reference problems reminds me of another context which seems that it encourages mid-stream pronoun switches: cooking shows. The following example is typical:
When you're mixing in the liquid ingredients, I always try to stir from the bottom to make sure they're well incorporated.
These "when you [X], I [Y]" statements, where "you" and "I" refer to the same person, are extremely common in instructional contexts. I suspect that they are generally a result of politeness: you need to tell people what to do, but you don't want to come off as bossy—so instead, you helpfully share how you personally would do it. This is similar to an indirect command, in which the command is put into an impersonal form, to avoid making direct orders. This is one step more removed, though: here, no desire for future actions is expressed at all, just a seemingly innocent statement about what the speaker usually does. We need a term for this phenomenon, in which the agent is changed to avoid using an imperative. I suggest the "passive aggressive voice."
Not all such examples can be attributed to politeness, however. Sometimes it seems to be a more general interchangeability of "generic you" and "generic I", as seen in the following quote from an interview with Grant Aleksander:
When you're asked to submit something, I always try to find an episode where the writing is good. Because even if you don't do a particularly good job with it, the writing makes you look better. I'd always rather have a well-written episode than anything else...
(Maybe he finds it hard to imagine that he personally would not have done a good job with an episode—but he could easily see it happening to others.)
In the following quote about National Good Manners Day*, Bridget from the USA can't settle on who she's talking about, either:
When you're a nice restaurant, I always try to have better manners than I have at home. Everyone should have manners to some extent!
Example of this are a bit hard to find on Google, but I hear them all the time. My very favorite example occurred in a commercial for one of those Fox "reality dating" shows (Survivor Island? Fantasy Millionaire?) One of the contestants confessed that
If you kiss Jason, it's a very intimate thing for me.
(meaning when she kisses Jason—not that she gets a kick out of watching him kiss others) In this case, it's not politeness, but modesty that prompts the switch. It would seem too kiss-and-tell to say "When I'm kissing Jason...", but of course there's a limit to how far you can continue in the second person (?? "If you kiss Jason, it's a very intimate thing for you"). I don't know why she didn't just stop after "thing", but there you have it.