Thanks for your inquiry. I have tested the scenario and have managed to reproduce the same issue at my side. For the sake of correction, I have logged this problem in our issue tracking system as WORDSNET-11955. I have linked this forum thread to the same issue and you will be notified via this forum thread once this issue is resolved.
We apologize for your inconvenience.
Thanks for your patience. It is to update you that we have closed the issue (WORDSNET-11955) with ‘Won’t Fix’ resolution. Please note that Aspose.Words mimics the behavior of MS Word. PDF/A-1 was not designed for images with transparency. MS Word doesn’t produce the proper output also. You should either save the document without PDF/A compliance or use the images without the transparency in your document.