I have updated to v7.3.0, which is the latest I can go at present until we update our subscription, but the behaviour is exactly the same. I haven't been able to locate any release notes detailing the differences between 7.3.0 and 7.4.0 (which is what Nausherwan tried), but surely your engineers would know if they had fixed a bug of this magnitude between these releases?
In terms of you replicating it, I have previously uploaded some code which, if run, will call our mapping server four times for each image - I know this because I can monitor the mapping server. How you prove it I'm not sure, but I can assure you it's happening and causing the PDF to take a lot longer to render than we would like.
I get the impression that you think the image is being rendered four times (well it might be - one on top of the other). Each image is only shown once, but is fetched from the server four times.