TYPO3 Core

attached is a better patch, still not sure if valid for all situations.
Please give feedback, if you have the same behaviour like described in this issue and if the patch fixes it.

Depending on the feedback, i will send a review patch to gerrit.

Seems not present in 6.2.12: this is my test (fresh installation):

1) Typoscript Setup:

config.disablePrefixComment=1
page = PAGE

page.5 = HMENU
page.5.1 = JSMENU
page.5.1 {
  levels = 1
  1.wrap = |<br>
}
page.10 < styles.content.get

Result: (only jsmenu object):
In the head section:

<script type="text/javascript" src="typo3/sysext/frontend/Resources/Public/JavaScript/jsfunc.menu.js"></script>

<script type="text/javascript">
    /*<![CDATA[*/
<!--
var JSmenub9af9 = new JSmenu(1, 'JSmenub9af9Form');
 var eidb9af91=0;
eidb9af91=JSmenub9af9.add(0,0,0,'level1','index.php?id=8','');
eidb9af91=JSmenub9af9.add(0,eidb9af91,0,'my\u0020page','index.php?id=2','');
eidb9af91=JSmenub9af9.add(0,eidb9af91,0,'my\u0020page\u00202','index.php?id=4','');

// -->
    /*]]>*/
</script>

In the body section:

<form action="" method="post" style="margin: 0 0 0 0;" name="JSmenub9af9Form">
    <select name="selector1" onchange="JSmenub9af9.act(1);">
        <option value="0">______________</option>
        <option value="0"></option>
        <option value="0"></option>
        <option value="0"></option>
        <option value="0"></option>
    </select><br>
</form>
<script type="text/javascript"> /*<![CDATA[*/ JSmenub9af9.writeOut(1,JSmenub9af9.openID,1); /*]]>*/ </script>

2) add the FELOGIN plugin in page colunm0;

result (I also cleared the cache):

head section:

<script type="text/javascript" src="typo3/sysext/frontend/Resources/Public/JavaScript/jsfunc.menu.js"></script>

<script type="text/javascript">
    /*<![CDATA[*/
<!--
var JSmenu96094 = new JSmenu(1, 'JSmenu96094Form');
 var eid960941=0;
eid960941=JSmenu96094.add(0,0,0,'level1','index.php?id=8','');
eid960941=JSmenu96094.add(0,eid960941,0,'my\u0020page','index.php?id=2','');
eid960941=JSmenu96094.add(0,eid960941,0,'my\u0020page\u00202','index.php?id=4','');

// -->
    /*]]>*/
</script>

<script type="text/javascript">var TYPO3FrontendLoginFormRsaEncryptionPublicKeyUrl = 'index.php?eID=FrontendLoginRsaPublicKey';</script>
<script type="text/javascript" src="http://typo3.62.basic.it:8888/typo3/sysext/rsaauth/resources/jsbn/jsbn.js"></script>
<script type="text/javascript" src="http://typo3.62.basic.it:8888/typo3/sysext/rsaauth/resources/jsbn/prng4.js"></script>
<script type="text/javascript" src="http://typo3.62.basic.it:8888/typo3/sysext/rsaauth/resources/jsbn/rng.js"></script>
<script type="text/javascript" src="http://typo3.62.basic.it:8888/typo3/sysext/rsaauth/resources/jsbn/rsa.js"></script>
<script type="text/javascript" src="http://typo3.62.basic.it:8888/typo3/sysext/rsaauth/resources/jsbn/base64.js"></script>
<script type="text/javascript" src="http://typo3.62.basic.it:8888/typo3/sysext/rsaauth/resources/FrontendLoginFormRsaEncryption.min.js"></script>

body section:

<form action="" method="post" style="margin: 0 0 0 0;" name="JSmenu96094Form">
    <select name="selector1" onchange="JSmenu96094.act(1);">
        <option value="0">______________</option>
        <option value="0"></option>
        <option value="0"></option>
        <option value="0"></option>
        <option value="0"></option>
    </select><br>
</form>
<script type="text/javascript"> /*<![CDATA[*/ JSmenu96094.writeOut(1,JSmenu96094.openID,1); /*]]>*/ </script>

If you think that this is the wrong decision or experience this issue again, then please write to the mailing list typo3.teams.bugs with issue number and an explanation or open a new ticket and add a relation to this ticket number.