This sounds like an unintentional side effect of "shortening" host names. In many cases, such as AWS EC2 host names (example: ec2-55-111-222-333.compute-1.amazonaws.com), we want to trim those redundant / repetitive suffixes to display a smaller prompt. Does not work great for IP addresses though.

A patch for the issue below.

Please note that this aims to be a very simple solution: a name like 123.456.com would not be shortened to 123.

Numeric host (and domain) names are legal (except for the top level domain). Nevertheless numeric host names are very rare and entering IP addresses for the host connection is common.

Taking care of the 123.456.com case would make the code more difficult to understand and verify (by using regular expressions or testing the right hand side of the host name while making sure it's not already a short name).

@@ -893,6 +893,8 @@
         host = self.pgexecute.host or '(none)'
         string = string.replace('\\H', host)
         short_host, _, _ = host.partition('.')
+        if short_host.isdigit():
+            short_host = host
         string = string.replace('\\h', short_host)
         string = string.replace('\\d', self.pgexecute.dbname or '(none)')
         string = string.replace('\\p', str(self.pgexecute.port) or '(none)')