There's undoubtedly a name for this phenomenon, and if there isn't, the Language Log folks can come up with one in a jiffy. What's happening is that a word with an uncontroversial past tense (verbs) or plural (nouns) is used in a new context. The new context can be a new definition (e.g. a computer mouse) or with some sort of morphological twist (trouble+shoot). The new context is just sufficiently different to cause speakers to think of the word as new, or at least, to not intuitively connect it to its related form.
Some examples that I've noted here before (I think):
- Plural of (computer) mouse: mice or mouses? Contemplated at leisure, it's easy to be confident that you know. But there is that "No, wait ..." factor, and Google lists nearly 2 million hits for mouses.
- In baseball, today a hitter flies out; yesterday he flied out.
- The past of cast is cast, but the past of podcast and broadcast is very often -casted.
Update 10/17/06: Saw the past of to cheerlead in the New Yorker recently: they cheerlead. Again, correct per the stem, but still a "No, wait ..." moment.
This phenomenon really only occurs when the original word has some sort of irregularity to it -- for example, the past of shoot is shot (irregular), not shooted (regular). But in the new context, folks apply the rules for formation of new words, which are overwhelmingly to use regular inflections and declensions and conjugations. New nouns are pluralized by adding -(e)s -- whatever your classics teacher might have told you, the common plural in English of octopus is octopuses. New verbs form the past tense with -d/-ed -- if we make up a new verb to bim, its past tense is going to be bimmed. (A form of not particularly hilarious humor is to apply faux irregular rules to regular verbs, e.g., squeeze-squoze, think-thunk, bring-brang, status-stati, etc.)
There is a certain, mmm, class of people who look down on this type of formation, but I don't see any particular reason why that should be. When little kids do it, we think it's cute, although the more appropriate sentiment might be astonishment at how quickly and thoroughly small children deduce morphological rules. And anyway, did you have a "No, wait ..." moment when you thought about troubleshoot? All right, then.
 A pattern that can throw people is a verb whose root contains -ing, like ring, sing, or fling. Make up a verb with -ing (e.g., fring), and a certain number of people will intuitvely use the irregular past. See Pinker in Rules and Words (or equivalent).
 A few times these forms have scrabbled their way into acceptance, the commonly cited example always being snuck in place of the (nominally) historically correct sneaked. Also: quit (vs. quitted), knelt (vs. kneeled), drug (vs. dragged).