I create a listener, and I can go through all the settings, but I need to be able to add a fourth server to the definition. There's a "+" below it but while it adds (part of) a line, entering anything in here doesn't result in the desired configuration.

Example;

Adding a fourth server results in;

Note the line appears "incomplete" and contains another "+" at the end of the line. Clicking that results in another incomplete line;

It also doesn't matter what data I put in this line, no additional server definition is added to the HAProxy definition. I have to edit the configuration manually to add that fourth server, which of course gets overwritten if I have to change the definition.