I can't reproduce it.
Could you check again?

what you mean check again? i tried to save job and other job like several times (actually more than ~30 times!) and with different combinations (guessed maybe some option needs to be on), so i don't think it will change unless there's some debug to see or new version, maybe show config.xml for the job? what to expect there or how to dump whatever it is supposed to save to ...?

i checked again. removed all $JENKINS_DIR content, and added completely new job. the ETag and MTime checkboxes do not get saved. this is the content of config.xml after i submitted the form first time by checking the checkboxes:

<?xml version='1.0' encoding='UTF-8'?>
<project>
<actions/>
<description>poll an url</description>
<keepDependencies>false</keepDependencies>
<properties/>
<scm class="hudson.scm.NullSCM"/>
<canRoam>true</canRoam>
<disabled>false</disabled>
<blockBuildWhenDownstreamBuilding>false</blockBuildWhenDownstreamBuilding>
<blockBuildWhenUpstreamBuilding>false</blockBuildWhenUpstreamBuilding>
<triggers class="vector">
<org.jenkinsci.plugins.urltrigger.URLTrigger plugin="urltrigger@0.35">
<spec>* * * * *</spec>
<entries>
<org.jenkinsci.plugins.urltrigger.URLTriggerEntry>
<url>http://requestb.in/1ecdiq91</url>
<proxyActivated>false</proxyActivated>
<checkStatus>false</checkStatus>
<statusCode>200</statusCode>
<timeout>300</timeout>
<checkETag>true</checkETag>
<checkLastModificationDate>true</checkLastModificationDate>
<inspectingContent>false</inspectingContent>
<contentTypes/>
</org.jenkinsci.plugins.urltrigger.URLTriggerEntry>
</entries>
<labelRestriction>false</labelRestriction>
</org.jenkinsci.plugins.urltrigger.URLTrigger>
</triggers>
<concurrentBuild>false</concurrentBuild>
<builders/>
<publishers/>
<buildWrappers/>
</project>

and when i open it again, checkboxes ARE NOT checked, and save:
<?xml version='1.0' encoding='UTF-8'?>
<project>
<actions/>
<description>poll an url</description>
<keepDependencies>false</keepDependencies>
<properties/>
<scm class="hudson.scm.NullSCM"/>
<canRoam>true</canRoam>
<disabled>false</disabled>
<blockBuildWhenDownstreamBuilding>false</blockBuildWhenDownstreamBuilding>
<blockBuildWhenUpstreamBuilding>false</blockBuildWhenUpstreamBuilding>
<triggers class="vector">
<org.jenkinsci.plugins.urltrigger.URLTrigger plugin="urltrigger@0.35">
<spec>* * * * *</spec>
<entries>
<org.jenkinsci.plugins.urltrigger.URLTriggerEntry>
<url>http://requestb.in/1ecdiq91</url>
<proxyActivated>false</proxyActivated>
<checkStatus>false</checkStatus>
<statusCode>200</statusCode>
<timeout>300</timeout>
<checkETag>false</checkETag>
<checkLastModificationDate>false</checkLastModificationDate>
<inspectingContent>false</inspectingContent>
<contentTypes/>
</org.jenkinsci.plugins.urltrigger.URLTriggerEntry>
</entries>
<labelRestriction>false</labelRestriction>
</org.jenkinsci.plugins.urltrigger.URLTrigger>
</triggers>
<concurrentBuild>false</concurrentBuild>
<builders/>
<publishers/>
<buildWrappers/>
</project>

This plugin does not work at all for me, even content check is not saved and thus not working.
no build is triggered!

Jenkins ver: 1.509.3
Jenkins URLTrigger Plug-in: 0.35

urltrigger log:

[URLTrigger] - Poll with a URL

Polling started on Sep 23, 2013 12:01:39 AM
Polling for the job xtables-geoip
Looking nodes where the poll can be run.
Looking for a candidate node to run the poll.
Looking for a node with no predefined label.
Trying to poll with the last built on node.

Polling on master.
Invoking the url:
http://geolite.maxmind.com/download/geoip/database/GeoIPCountryCSV.zip
Invoking the url:
http://geolite.maxmind.com/download/geoip/database/GeoIPv6.csv.gz

Polling complete. Took 0.47 sec.
No changes.

JENKINS-20712 was fixed