@Alex Earl - Currently, I upgraded my email-ext plugin to v2.34, where i am not seeing this problem.
I got this when I followed the workaround provided by Jhon Cruz and restarted my jenkins.
However..
<?xml version='1.0' encoding='UTF-8'?>
<hudson.plugins.emailext.ExtendedEmailPublisherDescriptor plugin="email-ext@2.34">
<hudsonUrl>http://ci.net/</hudsonUrl>
<adminAddress>Jenkins@test.com</adminAddress>
<smtpHost>gmail-smtp-in.l.google.com</smtpHost>
<useSsl>false</useSsl>
<defaultContentType>text/plain</defaultContentType>
<defaultSubject>$PROJECT_NAME - Build # $BUILD_NUMBER - $BUILD_STATUS!</defaultSubject>
<defaultBody>$PROJECT_NAME - Build # $BUILD_NUMBER - $BUILD_STATUS:

Check console output at $BUILD_URL to view the results.</defaultBody>
<defaultPresendScript></defaultPresendScript>
<maxAttachmentSize>-1</maxAttachmentSize>
<recipientList></recipientList>
<defaultReplyTo></defaultReplyTo>
<excludedCommitters></excludedCommitters>
<overrideGlobalSettings>true</overrideGlobalSettings>
<precedenceBulk>false</precedenceBulk>
<debugMode>false</debugMode>
<enableSecurity>false</enableSecurity>
<enableWatching>false</enableWatching>
</hudson.plugins.emailext.ExtendedEmailPublisherDescriptor>
I cannot downgrade again now.
This looks like a completely different problem. Please post your hudson.plugins.emailext.ExtendedEmailPublisher.xml file.