We only "optimistically retry connections" once if we have other bridges descs
Start your Tor Browser using obfs3 bridges. Now you'll have descriptors for these obfs3 bridges in your state file.
Then restart and use meek bridges. Now you'll have both.
Then use meek until something times out and your Tor client marks your single meek bridge as down.
Then on the next request you make, your Tor will realize that all your bridges are down, and print out
"Application request when we haven't used client functionality " "lately. Optimistically trying known %s again.", options->UseBridges ? "bridges" : "entrynodes");
and call entries_retry_all().
Then entries_retry_helper() will walk through your list of entry_guards, and call router_set_status(node->identity, 1) on all of them -- including your obfs3 bridges!
Then use your Tor Browser a while more, until something else times out and your single meek bridge gets marked as down again.
Then on the next request you make, your Tor doesn't realize that all your bridges are down, since your obfs3 bridges are listed as running. So it just sits there wondering why it can't make a circuit. Oops!