At this point, you have two choices:
- Log it separately, and risk creating a duplicate
- Log it in the existing issue, and risk conflating two issues into one
Either way, you're taking a risk: of a duplicate, or of a false reopen. So what do you do?
Go with the risk of a duplicate, because duplicates are cheaper.
Let's say that risk is realized, and the bug is a duplicate. Now you have to close the bug as a duplicate, and reference the duplicate bug from the original. Annoying, sure, and a little bit of time wasted confirming that the bug is a duplicate, but in the grand scheme of things, not a big deal.
If you'd gone the other way, and reopened a bug, you might have realized the risk associated with that: maybe it's a different bug. In this case you have to open a new bug, comment/edit/delete the erroneous reporting in the old bug, close the old bug again, and move any referenced logs or other information. Oh yeah, and now the developer who closed the bug is just a little bit insulted that you thought his fix was incomplete.
If you're very sure that the same root cause underlies two failures, please go ahead and reopen the bug. If you're not sure - like our "connection refused" example, which could have several different causes ranging from network failure to configuration problem to server failure - go ahead and log a new bug. It's easier to find out you have a duplicate than to peel apart two bugs that got conflated into one.