I did some testing using your demo and found there is a problem with image alignment in both the output files and upon re-editing of an previously ordered document.

I made a design template using the template manager by uploading a Hi Res jpg file with gray boxes to indicate where the customer should place there images on the document and saved it.
Then I opened the product on the site as a customer would and clicked the Start Design then placed images on top of the gray boxes aligning them to each other using the layout guides generated from your plug-in and hit the process button and completed the order.

On the order details page is a link that allows the customer to download the file in PNG JPG and PDF formats. I downloaded all formats and the images and were out of alignment with each other in all output files especially the PDF file which is my preferred format, with the PNG being the best. Additionally when I open the Edit Design link on the Order Detail page the same design file from the order shows the same alignment issue.

Is this an issue with the demo I’m using or is it something else?
I plan on using this plug-in on multiple domains so I need to make sure it works properly, the proper alignment of elements is very important for my products. 

Could you please let me know what can be done to prevent this?