after a recent episode of sleep walking around the dorm, there's been a lot of cause for people to use the past participle of 'to sleep walk.' The past participle is apparently NOT 'sleep walked,' but 'slept walked,' or 'slep walked.' this phenomena is VERY wide-spread around here. I'd estimate at least a dozen people have understood and used these forms in the last few days.
no observed forms so far have dropped the 'ed' from 'walked' and marked only the vowel change and 't' ending on 'sleep,' leading me to wonder why the construction ends up with this double-marking. if it's treated as a single lexical item, then the vowel change makes a lot of sense (witness the two changes from 'sleep' to 'slept'). This is the best explanation i've thought of so far...
a google search for 'slept walked' returned almost 10,000 hits, some hyphenated, mostly from xangas. and a search for 'slep walked' asked 'did you mean 'slept walked'? this leads me to believe that the difference between the two is just the result of a phonological change, and that writers believe 'slept walked' is the proper form. 'sleepwalked,' however, still seems to be the dictionary-sanctioned form, returning 54,000 hits. 'sleep walked' had 23,000 hits, and a suggestion for the one-word variant.
comparison to other verbs hasn't helped much yet. the most similar construction i can think of is 'to speed walk,' and i'm fairly certain most speakers would find '*he sped walked' incorrect. it yields only 233 google hits. send in your examples, if you've got 'em!