I may have missed something, but I can't reproduce the issue.

Here is what I tested:

Full nginx config file:

worker_processes  1;
events {
    worker_connections  1024;
}
http {
    include       mime.types;
    default_type  application/octet-stream;
    sendfile        on;
    keepalive_timeout  65;
    
    server {
        listen       80;
        location /comics {
            proxy_pass http://10.0.0.3:2202;
            proxy_set_header Host $host;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Real-IP $remote_addr;
        }        
        
        location /comics/admin {
            proxy_pass http://10.0.0.3:2203;
            proxy_set_header Host $host;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Real-IP $remote_addr;
        }
    }
}

Direct access to Ubooquity:

Access through Nginx:

Your Java version is fine, and Windows 7 should not be an issue either. I'm sorry, I don't know what's going on. :(

Could you give me your nginx config (the part that for the reverse proxy) ?

Yes, there seem to be something seriuosly wrong with your installation.

Do you run Ubooquity on a recent version of Java 8 ? (I haven't tested it with Java 9)

Your arguments are valid, but I still believe they don't outweigh the advantages of embedded metadata.

I created an entry in my backlog to add external OPF support in Ubooquity, but since this is a very specific scenario, it's unlikely to be implemented anytime soon.

Ubooquity provides a standard OPDS feed. See the specs here:

http://opds-spec.org/specs/opds-catalog-1-1-20110627/

In this feed, it provides an additional link to allow the client to read pages directly.

The specs of this extensions are here:

http://vaemendis.net/opds-pse/

I guess I'm going to need an explanation with a few examples, I'm not sure I understand what you mean.

try:

.*pdf

(careful, the "." is before the "*")

Yep, I know this issue, but I put it aside for more urgent bugs/feature.

If someone wants to take a look at the code (the JS can be seen in your browser) and give me the fix...

Indeed. There is no way around that unfortunately.