Lightroom Asset API Flag Option not working as Expected

I am using the Lightroom API to list the assets of an album.

https://www.adobe.io/apis/creativecloud/lightroom/apidocs.html#/

For an album that I am testing that has 7 assets, one with the Pick flag and one with the Reject Flag.

https://lr.adobe.io/v2/catalogs/7afe0a02a277465eb76b99c90193a430/albums/778ef65e2c6f4d9192600214a8ad10a0/assets?limit=500&hide_stacked_assets=true&flag=unflagged;pick

return 5 results (the unpicked assets) – where it should return 6. – as I want to get all the assets that are either picked or unflagged.

https://lr.adobe.io/v2/catalogs/7afe0a02a277465eb76b99c90193a430/albums/778ef65e2c6f4d9192600214a8ad10a0/assets?limit=500&hide_stacked_assets=true&flag=pick;unflagged

returns 1 result(the picked asset) – where it should return the same 6.

This is the documentation for the flag parameter:

Semi-colon separated review flag values used to filter assets returned. Can be combined with subtype filter. Valid values for flags are 'pick’, ‘unflagged’ and 'reject’. This parameter cannot be used along with album_filters parameter. Default behavior is to display all assets.

Please advise – is this a bug or am I using the API incorrectly?

Thanks,

Michael