If i have changed the watermark option and do it on the image add watermark the plugin get the image already watermarked and readd the watermark.
For this problem i disable the plugin, enable the regenerate thumbnails and regenerate the image. After renable this plugin and disable the regenerate thumbnails. Finally i add the watermark to the cleaned image.
PS: the full size are not watermarked for readd the watermark with this method.