Specification for File.createTempFile(prefix, suffix, dir) reads:
"To create the new file, the prefix and the suffix may first be adjusted to fit the limitations of the underlying platform." And then specification explains how to deal with too long prefix and suffix. But it's not clear from specification how symbols that are illegal for underlying filesystem should be treated. Whether they should be omitted, replaced or IOException should be thrown.

We have challenge 6416299 on tck_cdc for this ambiguity.