JIRA Issue Details panel breaks when JIRA Agile ranking is broken

2014-03-20 16:59:43,399 http-apr-8080-exec-20 ERROR pt100945 1019x11765x2 ew1xyx 10.152.164.34,127.0.0.1 /browse/PONY-49 [jira.web.component.ModuleWebComponentImpl] Error rendering web panel: com.atlassian.jira.jira-view-issue-plugin:details-module (null)
com.atlassian.greenhopper.service.rank.RankException: Multiple heads found in rank chain: issueIDs [[634166 r0 no prev n634164], [631373 r0 no prev n631375]] have no parent link. Please update the rank table and ensure that there is exactly one issue that has no child and exactly one that has no parent.
	at com.atlassian.greenhopper.service.rank.RankIndexBuilder.validate(RankIndexBuilder.java:166)
	at com.atlassian.greenhopper.service.rank.RankIndexBuilder.build(RankIndexBuilder.java:85)
	at com.atlassian.greenhopper.service.rank.RankIndexServiceImpl$RankIndexSupplier.get(RankIndexServiceImpl.java:417)
	at com.atlassian.greenhopper.service.rank.RankIndexServiceImpl$RankIndexSupplier.get(RankIndexServiceImpl.java:388)
	at com.google.common.base.Suppliers$MemoizingSupplier.get(Suppliers.java:109)
	at com.atlassian.greenhopper.service.rank.RankIndexServiceImpl.getIndex(RankIndexServiceImpl.java:385)
	at com.atlassian.greenhopper.service.rank.RankIndexServiceImpl.fetchCreate(RankIndexServiceImpl.java:348)
	at com.atlassian.greenhopper.service.rank.RankIndexServiceImpl.getIssuePosition(RankIndexServiceImpl.java:80)
	at com.atlassian.greenhopper.customfield.rank.RankCFType.getValueFromIssue(RankCFType.java:42)
	at com.atlassian.jira.issue.fields.CustomFieldImpl.getValue(CustomFieldImpl.java:384)