too many words by laura lemay

there is a word for that

Vorführeffekt [vor-fyur-ef-ekt]

a German word, literally ‘presentation effect’ which describes a problem, usually with a computer, that doesn’t happen when other people try to replicate it (such as, say, the Help Desk guy).

(I got it from Erin’s Weird and Wonderful Word of the Day{.broken_link})