Funny definition of 'bug'. 
It's not a bug. Not everything in the default toolbars is in the Customize / Commands list. (Although most of the elements in the FTP menu are in the list, FWIW. Type 'ftp' into the filter.)
You can quickly reset a toolbar to defaults via the menu you get when you right-click an empty part of it.
Or, if you don't want to lose other changes, take this and paste it on to your toolbar:
<?xml version="1.0"?>
<button backcol="none" display="icon" dropdown_glyph="yes" label_pos="right" separate="yes" textcol="none" type="menu">
<label>FT&P</label>
<icon1>#ftp</icon1>
<button backcol="none" display="both" hotkey="ctrl+Q" label_pos="right" separate="yes" textcol="none">
<label>&FTP Connect...\tCtrl+Q</label>
<tip>Connect to an FTP site</tip>
<icon1>#ftpconnect</icon1>
<function type="normal">
<instruction>Go FTP</instruction>
</function>
</button>
<button backcol="none" display="both" label_pos="right" textcol="none">
<label>&Add to Address Book</label>
<tip>Add the current FTP site to the Address Book</tip>
<icon1>#ftpaddsite</icon1>
<function type="normal">
<instruction>Prefs ADDFTPSITE</instruction>
</function>
</button>
<button backcol="none" display="both" hotkey="ctrl+shift+Q" label_pos="right" textcol="none">
<label>&Edit Address Book...\tCtrl+Shift+Q</label>
<tip>Opens the FTP Address Book editor</tip>
<icon1>#ftpaddressbook</icon1>
<function type="normal">
<instruction>Prefs FTPSITES</instruction>
</function>
</button>
<button backcol="none" display="both" label_pos="right" separate="yes" textcol="none">
<label>&Site Properties</label>
<tip>Shows properties dialog for the current FTP site</tip>
<icon1>#ftpsiteproperties</icon1>
<function type="normal">
<instruction>Properties FTPSITE</instruction>
</function>
</button>
<button backcol="none" display="label" label_pos="right" separate="yes" textcol="none">
<label>FTP Addresses</label>
<tip>Shows a list of your FTP addresses</tip>
<function type="normal">
<instruction>Go FTPSITELIST FTPSITEICONS USEQUALKEYS</instruction>
</function>
</button>
<button backcol="none" display="both" label_pos="right" textcol="none">
<label>&Display FTP Logs</label>
<tip>Displays the logs of FTP activity</tip>
<icon1>#logs</icon1>
<function type="normal">
<instruction>Set UTILITY=FTPLog,Toggle</instruction>
</function>
</button>
</button>