It would be wrong to imagine that the stress pattern is always fixed and unchanging in English words. Stress position may vary for one of two reasons: either as a result of the stress on other words occurring next to the word in question, or because not all speakers agree on the placement of stress in some words. The former case is an aspect of connected speech that will be encountered again: the main effect is that the stress on a final-stressed compound tends to move to a preceding syllable and change to secondary stress if the following word begins with a strongly stressed syllable. Thus (using some examples):

,bad-'tempered                 but        a ,bad-tempered 'teacher           

.half-'timbered                  but        a ,half-timbered 'house

.heavy-'handed                 but        a .heavy-handed 'sentence

The second is not a serious problem, but is one that foreign learners should be aware of. A well-known example is 'controversy', which is pronounced by some speakers as 'kQntr@v³:si and by others as k@n'trQv@si; it would be quite wrong to say that one version was correct and one incorrect. Other examples of different possibilities are 'ice cream' (either ,aɪs kri:m or 'aɪs kri:m),'kilometre' (either kɪ'ɪɒmɪtə or 'kɪləmi:tə) and 'formidable' ('fɔ:mɪdəb_וl or fo:'mɪdəb_וl).