[Mediawiki-api] Why does 1.26 API return hash when 1.24 returned array?

I'm upgrading my site to MediaWiki 1.26 (from 1.24) and noticed a change in API behavior. One of our custom API modules:

http://mywiki.com/w/api.php?action=foobar&format=json......

used to return a JSON array, like this:

[ {"start":"2015-12-28","end":"2016-01-01", ...} ]

and now it returns a numerically indexed hash like this instead:

{"0":{"start":"2016-01-18","end":"2016-01-18", ...}}

Do we need to do something special in 1.26 to get the array instead of the hash? Or is this a breaking change? Or are we probably doing something wrong? I looked for breaking API changes in 1.25 and 1.26 but don't see anything like this:

https://www.mediawiki.org/wiki/MediaWiki_1.25#API_changes https://www.mediawiki.org/wiki/MediaWiki_1.26#API_changes

Thanks, DanB