Thanks for the details!
When the field is set to 1, comments will be synced the next time the page is loaded. When the comments are synced the value of wpdc_sync_post_comments will be set back to 0.
From looking at the metadata you posted, it seems that the plugin is subtracting 1 from the comments number when it shouldn’t be. I’ve been travelling for the past couple of days. I’ll look at this closely when I get back to work tomorrow.