I've been through the documentation several times and haven't found anything to address this.
I can't ever get more than 256 changesets back from the API. It doesn't matter how I call the API. I've tried getting 255 changesets, then setting the $skip parameter to 255 and getting the next 255 changesets, but the second call only returns 1 changeset.
Is this an intentional limitation of the API? This is a deal-breaker for us. If we can't more changesets, we'll have to move to another provider, like Atlassian Jira/Stack.