Json help on Shield

[mpg732]

Running the latest on every thing on a shield pro, working on an interface for control, this command

{"jsonrpc":"2.0", "method":"Player.Seek", "params": { "playerid":1, "value":{ "seconds": 60 } }, "id":1}

will jump 60 seconds forward, but this command willnot but instead jump to 30 seconds into the video,

{"jsonrpc":"2.0", "method":"Player.Seek", "params": { "playerid":1, "value":{ "seconds": 30 } }, "id":1}

but this command will work jumping 30 seconds back,

{"jsonrpc":"2.0", "method":"Player.Seek", "params": { "playerid":1, "value":{ "seconds": -30 } }, "id":1}

any idea why?
Thanks
Mike