The non-determinism is from in which order tasks are run, buildprops can be before or after compile, each of these tasks contributes one jar belonging to the target.
If buildprops is run first, it will get the -0 suffix, and if subsequent run switches the order, it will get -1 suffix, but passes invalidation check, i.e, vt.valid = True, so -1 file is not created and eventually fail with file not found error.