There are many interesting events in the history of the English language. Which one of them gave us “defect” (noun,
/diːˈfɛkt/, imperfection) and “defect” (verb,
/dɪˈfɛkt/ , change allegiances)?
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(This is an expanded version of my earlier comment on the question.)
This is not the direct answer to your question, but anyway it seems pretty relevant.
In English, there are many two-syllable words which have an accent on the first syllable when used as a noun and on the second syllable when used as a verb, and “defect” is one of them. According to web search, such words seem to be known as “initial-stress-derived nouns.”
Wikipedia gives some explanation for this phenomenon: