Can you provide the step-by-step configuration? If you are using PAC, and the implementation is standards compliant, then the failed connection causes PAC to mark it as unavailable. If you have multiple servers it will failover.
You might even see this behavior if your PAC file returns a list-of-one. If so, it is time to start looking around for a reset button in the UI.
Here is what the spec said...which is really hard to find since AOL "lost" it from the legacy Netscape servers.
Here's a copy I saved before it fell out of the Google cache:
If there are multiple
semicolon-separated settings, the
left-most setting will be used, until
the Navigator fails to establish the
connection to the proxy. In that case
the next value will be used, etc. The
Navigator will automatically retry a
previously unresponsive proxy after 30
minutes, then after 1 hour from the
previous try (always adding an extra
30 minutes). If all proxies are down,
and there was no DIRECT option
specified, the Navigator will ask if
proxies should be temporarily ignored,
and direct connections attempted. The
Navigator will ask if proxies should
be retried after 20 minutes has passed
(then the next time 40 minutes from
the previous question, always adding
Anyhow, the selection of the timeout values was rather arbitrary (this was meant to be a working description of what was to be implemented, and never scrutinized as an RFC). Most vendors that worked on this made modifications to actual failover or timeouts, for practicality (including Mozilla's re-write of the original Navigator PAC).
(This might be hearsay, but I know most of this because had various conversations with the authors when I worked for Netscape and mozilla.org).
I never tested/used Opera much, but check your documentation for more info. If Opera is responsive as a vendor, lean on them for more details. This is the kind of stuff where people should be more clear about what their software does.