Curious things happen, if one supplies code to the parallelizer that does not make sense. If the loop code touches variables that are never used, various strange results can occur. This is not a huge problem par se, but it is something that must be taken into account, at least when we get a reasonable high-level front end language and a compiler for that.
It is actually another strength of this language, that we can easily spot superfluous instructions and remove them. This is not currently done, but it's another one of those fairly easy to implement tasks, that are just waiting to happen.