I’m pretty sure Bonds Beyond Time had an equally oddball release of its home video release.
An article by TV Asashi about Mother’s Day, confirms in one of the sentences that Dark Side of Dimensions will not be released in Japan on DVD and Blu-Ray until 2017.
No reason was given for the 8+ month delay.
But it is noted that the English version of the movie won’t be available until 2017 either, so it’s possible the two dates are related.