Mercurial repository can't connect to passphrased bitbucket ssh account

Steps to reproduce:
1. Create new plan
2.1. RepoUrl = ssh://hg@bitbucket.org/bamboo_tests/private
2.2. AuthType = SSH_PROXY (a.k.a. keyfile with passphrase)
2.3. Keyfile = grab it from bamboo-trunk/bamboo-acceptance-test/src/it/resources/bamboo_tests_id_rsa - should work.
3. Launch the plan. Repeat launching until error is encountered.

System Error Details

(com.atlassian.bamboo.plugins.hg.HgCommandException : command [hg, id, -i, --debug, --rev, default, --config, ui.ssh=ssh -o StrictHostKeyChecking=no -o BatchMode=yes, ssh://abafddba-fc0f-4756-b8f5-8ada124ad70b@127.0.0.1:56280/bamboo_tests/private] failed. Working directory was `/home/pstefaniak/bamboo/atlassian-bamboo-2.7-standalone/bamboo-home/xml-data/build-dir/_hg-repositories-cache/0x9497f23a-1/repository'. stderr: SSH Proxy error: Authenticating remote session failed stdout: running ssh -o StrictHostKeyChecking=no -o BatchMode=yes abafddba-fc0f-4756-b8f5-8ada124ad70b@127.0.0.1 -p 56280 "hg -R bamboo_tests/private serve --stdio" sending hello command sending between command remote: [hg@bitbucket.org/207.223.240.182:22] Authenticating remote session failed )
Occurred: 29 Dec 2010, 4:22:11 PM

---

com.atlassian.bamboo.plugins.hg.HgCommandException: command [hg, id, -i, --debug, --rev, default, --config, ui.ssh=ssh -o StrictHostKeyChecking=no -o BatchMode=yes, ssh://abafddba-fc0f-4756-b8f5-8ada124ad70b@127.0.0.1:56280/bamboo_tests/private] failed. Working directory was `/home/pstefaniak/bamboo/atlassian-bamboo-2.7-standalone/bamboo-home/xml-data/build-dir/_hg-repositories-cache/0x9497f23a-1/repository'. stderr: SSH Proxy error: Authenticating remote session failed stdout: running ssh -o StrictHostKeyChecking=no -o BatchMode=yes abafddba-fc0f-4756-b8f5-8ada124ad70b@127.0.0.1 -p 56280 "hg -R bamboo_tests/private serve --stdio"
sending hello command
sending between command
remote: [hg@bitbucket.org/207.223.240.182:22] Authenticating remote session failed

	at com.atlassian.bamboo.plugins.hg.HgCommandProcessor.runCommand(HgCommandProcessor.java:317)
	at com.atlassian.bamboo.plugins.hg.HgCommandProcessor.extractTipHash(HgCommandProcessor.java:378)
	at com.atlassian.bamboo.plugins.hg.HgCommandProcessor.getRemoteTipForBranch(HgCommandProcessor.java:225)
	at com.atlassian.bamboo.plugins.hg.HgRepositoryAccessImpl.getLatestRemoteRevisionHash(HgRepositoryAccessImpl.java:238)
	at com.atlassian.bamboo.plugins.hg.HgRepositoryAccessImpl.collectChangesSinceLastBuild(HgRepositoryAccessImpl.java:85)
	at com.atlassian.bamboo.plugins.hg.HgRepository.collectChangesSinceLastBuild(HgRepository.java:234)
	at com.atlassian.bamboo.v2.trigger.DefaultChangeDetectionManager.collectChangesSinceLastBuild(DefaultChangeDetectionManager.java:92)
	at com.atlassian.bamboo.v2.trigger.ManualBuildDetectionAction.process(ManualBuildDetectionAction.java:80)
(...)
Caused by: com.atlassian.utils.process.ProcessException: Non-zero exit code: 255
	at com.atlassian.utils.process.PluggableProcessHandler.complete(PluggableProcessHandler.java:66)
	at com.atlassian.utils.process.ExternalProcess.finish(ExternalProcess.java:224)
	at com.atlassian.utils.process.ExternalProcess.execute(ExternalProcess.java:267)
	at com.atlassian.bamboo.plugins.hg.HgCommandProcessor.runCommand(HgCommandProcessor.java:312)
	... 161 more

Failure occurs near SshProxyCommand.java:168, finishWithError("Authenticating remote session failed", authFuture.getException());