Simply attaching gdb (then detaching immediately) to a running Percona mysqld instance causes Percona-server to disconnect clients. Same happens if you attach gdb then continue. Clients get "Lost connection to MySQL server during query" but reconnecting works fine and the server seem to be healthy after that. Using telnet to test shows the socket close when gdb attaches. This bug makes using "pstack", "poor man's profilier" or even Aspersa's "connect" tool impossible without disconnecting clients.
Percona-server 5.5.13 (installed from yum repo), CentOS 5.6 (running on EC2. also happens with Amazon AMI), gdb 7.0.1
Interestingly, it does not happen with original mysqld (5.5.10 from webtatic or 5.5.13 built from source).