Green rectangle beside tables in Kindle previewer?

Has anyone else seen this ‘green rectangle’ phenomenon using the Kindle Previewer application on Scrivener .mobi output? In short, when I use a two row, single column table to house a graphic and caption, I run into the only remaining challenge I have in getting Scrivener to produce mobi files that look the way I want them.

As any of you who create books with graphics know, the full-width graphics format for Kindles is 1200 pixels wide, and they strongly recommend using 300dpi. This works fine for all my graphics that are standalone, meaning without captions. I use the Mac Preview application to resize them to 1200 wide and 300 dpi. When I insert them in a Scrivener project, they are immediately too small, so I resize them there to 1200 wide again, which Scrivener then shows as being at 72 dpi. No worries as they have the correct resolution and look good in the Kindle previewer. They are all line drawings created in Inkspace. As Amazon recommends, I use PNG format in Scrivener.

All this changes when I use captioned images. I suppose I could just Gimp the caption into the image, now the books are final, but hey, i started with tables for this, and am reluctant to abandon them if I don’t have to. The issue seems to be that even when you set the border of a table to zero pixels, it still takes up some space. I am not sure why. I do note that the images are no longer aligned to the left margin, and nothing I have found seems to change that. by iterating the image sizes, I have found that once I go over 1020 pixels wide for an image in table, the Kindle previewer shows a green rectangle beside the table. Clicking on the rectangle simply moves it to the other side of the table. I have not found any reference to the rectangle in the Amazon documentation, or using a Google search. My suspicion is that it is there to indicate that your image is too wide to display.

I have attached an example below.

So… should I abandon tables for captioning images? Or is there some way to get an image in a table to go completely against the left margin?

(For the pedantic out there, I realize I will probably have to use Sigil for the final tweaks to the TOC and some other minor formatting aspects of the books.)

OK, in the absence of other advice, I have started to delete the tables and am replacing them by 1200-wide images that include the captions.