If you obfuscate the following code:

function test() {
    var importantVariableName = 'test';
    return importantVariableName.indexOf('test');
 }

with the following settings:

{
    deadCodeInjection: true,
    deadCodeInjectionThreshold: 1,
    debugProtection: true,
}

the variable name importantVariableName can be seen in clear text in the obfuscated code. This is the case even if the mangle and stringArrayEncoding options are used.

The named variable appears to be part of dead code since it is not set anywhere, but the obfuscated function call on it is still .indexOf('test').

Tested on version 0.11.2 and on https://javascriptobfuscator.herokuapp.com/