It turns out that the last comment was from a deleted user and that was causing it to crash, so I deleted that comment, and Jira wouldn't crash when trying to edit.

Is this actually getting fixed in the next release?

I have a similar problem, except Jira dies when trying to edit an issue where a deleted user has left comments. I hope it's related enough, that this bug will fix it.

com.atlassian.jira.issue.customfields.impl.FieldValidationException: User 'jamasters' was not found in the system.
at com.atlassian.jira.issue.customfields.converters.UserConverter.getUser(UserConverter.java:41)
at au.com.agiledigital.jira.plugin.LastUserCommentedCFType.getValueFromIssue(LastUserCommentedCFType.java:52)
at com.atlassian.jira.issue.fields.CustomFieldImpl.getCustomFieldParamsFromIssue(CustomFieldImpl.java:1039)
at com.atlassian.jira.issue.fields.CustomFieldImpl.populateFromIssue(CustomFieldImpl.java:526)
at com.atlassian.jira.issue.fields.screen.FieldScreenRenderLayoutItemImpl.populateFromIssue(FieldScreenRenderLayoutItemImpl.java:85)
at com.atlassian.jira.web.action.issue.EditIssue.doDefault(EditIssue.java:91)
at sun.reflect.GeneratedMethodAccessor1676.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at webwork.util.InjectionUtils$DefaultInjectionImpl.invoke(InjectionUtils.java:61)
at webwork.util.InjectionUtils.invoke(InjectionUtils.java:52)
at webwork.action.ActionSupport.invokeCommand(ActionSupport.java:417)
at webwork.action.ActionSupport.execute(ActionSupport.java:146)
at com.atlassian.jira.action.JiraActionSupport.execute(JiraActionSupport.java:54)
at webwork.dispatcher.GenericDispatcher.executeAction(GenericDispatcher.java:132)
at com.atlassian.jira.web.dispatcher.JiraServletDispatcher.service(JiraServletDispatcher.java:178)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

We also found that we couldn't move issues to new projects where a deleted user had left comments on a jira.

Unfortunately not. This is still outstanding.

Has this fix been incorporated into JIRA v3.12.2-#300?

The fix for this issue has not been able to make it into JIRA v3.12. We are hoping to incorporate it into v3.12.1. As of writing however, there are 163 items scheduled as Fix For v3.12.1. We will not be able to include all of them.

We see the same error in th elog during upgrade from version 3.8.1 to 3.11
2007-11-13 03:56:47,987 indexerPool-1-thread-9 WARN [issue.customfields.impl.AbstractSingleFieldType] Value stored in database is invalid
com.atlassian.jira.issue.customfields.impl.FieldValidationException: User 'rsky' was not found in the system
at com.atlassian.jira.issue.customfields.converters.UserConverter.getUser(UserConverter.java:41)
at com.atlassian.jira.issue.customfields.impl.UserCFType.getSingularObjectFromString(UserCFType.java:53)
at com.atlassian.jira.issue.customfields.impl.StringCFType.getObjectFromDbValue(StringCFType.java:25)
at com.atlassian.jira.issue.customfields.impl.AbstractSingleFieldType.getValueFromIssue(AbstractSingleFieldType.java:87)
at com.atlassian.jira.issue.fields.CustomFieldImpl.getValue(CustomFieldImpl.java:266)
at com.atlassian.jira.issue.index.indexers.impl.DefaultCustomFieldIndexer.addIndex(DefaultCustomFieldIndexer.java:50)
at com.atlassian.jira.issue.index.IssueDocument.getDocument(IssueDocument.java:34)
at com.atlassian.jira.issue.index.IssueDocumentBuilderImpl.get(IssueDocumentBuilderImpl.java:14)
at com.atlassian.jira.issue.index.SingleThreadedIssueIndexer$IssueAndCommentCreator.handleIssueIndexing(SingleThreadedIssueIndexer.java:404)
at com.atlassian.jira.issue.index.MultiThreadedIssueIndexer$IssueIndexerRunnable.run(MultiThreadedIssueIndexer.java:98)
at com.atlassian.jira.util.concurrent.BoundedExecutor$1.run(BoundedExecutor.java:39)
at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:665)
at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:690)
at java.lang.Thread.run(Thread.java:534)