Multiple image fields using plupload stores all uploaded files in 1 image field

In a node 2 fields:
field_gallery_1 / field type = image (multiple) / widget = plupload
field_gallery_2 / field type = image (multiple) / widget = plupload

When uploading an image in field_gallery_1, it also shows in field_gallery_2.
Uploading image 2 in field_gallery_2 shows also in field_gallery_1 upload.

End result is both images are stored in field_gallery_2.

I replaced both widgets with the default 'image' uploader - no problems.
So I guess I isolated this problem to this API.