Yes. There has been discussion of this somewhere (that I can't find just now). It also has the stress in the wrong place, as the stress should be on the first syllable. Neither rule is supposed to work with prefixes and suffixes. Both problems would be avoided anyway if we wrote it as two separate words, or hyphenated it. It is made from the Latin word dia 'day' and the Gaelic for the moon. There are several examples with suffixes where the rules cannot be applied, but most prefixes are hyphenated (such as an-diugh 'today'). These days of the week seem to have been left out.
In addition, the word was originally spelt dia in Old Irish, and that would also avoid the problem.