values not persisting in dropdown of optional block - jelly/jenkins

I have the following in config.jelly:

<f:block>
            <table style="width:100%" id="rpmParameters-generic">
                <j:set var="rpmParameters" value="${instance.rpmParameters}"/>
                <f:optionalBlock name="rpmParameters" checked="${rpmParameters != null}"
                                 title="Mandatory parameter for rpm/msi/zip artifacts only"
                                 help="/plugin/artifactory/help/common/help-rpmParameters.html">
                    <input type="hidden" name="stapler-class" value="org.jfrog.hudson.util.RpmParameters"/>
                    <f:entry title="Operating System">
                                <select class="setting-input" name="operatingSystem" value="${rpmParameters.operatingSystem}">
                                        <option value="rhel5">rhel5</option>
                                        <option value="linux">linux</option>
                                        <option value="solaris">solaris</option>
                                        <option value="windows">windows</option>
                                </select>
                        </f:entry>
                    <f:entry title="Architecture">
                                <select class="setting-input" name="architecture" value="${rpmParameters.architecture}">
                                        <option value="i386">i386</option>
                                        <option value="x86_64">x86_64</option>
                                        <option value="no arch">no arch</option>
                                </select>
                        </f:entry>
                </f:optionalBlock>
            </table>
        </f:block>

The problem is that the checkbox for optional block persist when I hit save but for some reason the dropdown values of operating system and architecture don't persist in the UI after I save and reopen configuration.

Any idea why ?