V2 API: GET /posts using paramers 'offset' and 'tag' doesn't response posts by correct offset start

[alexhmm]

When creating an issue, please supply as much information as possible, such as the API request you tried, the response you received from the API, what you expected, what API client you are using, etc.

https://www.tumblr.com/docs/en/api/v2#posts--retrieve-published-posts

Bug description

When using api call GET /posts with request parameters offset and tag the response posts starting at a different (and randomly?) position from what is set in offset.
Iterating through posts with the same tag will return in double, triple. etc... occurrences

--> Example call: https://api.tumblr.com/v2/blog/xxx.tumblr.com/posts/?api_key=xxx&offset=5&tag=berlin

Offset is working fine without using the tag request parameter though.

Expected Behaviour:

GET /posts should response the correct offset starting position posts when using offset and tag request parameters.