Array.push(Object) inserts array of objects

I'm currently trying to read the days of absence of my colleague from our excel files and store them in a mongodb using mongoose and express-js.

Reading the data works fine, but updating the data in the db always produces the strange behavior, where inserting an Object into an array using Array.push() results in an Array of Objects containing a single object inside the outer array.

The function below gets the raw data from the excel files and attempts to store them in the db. Please ignore the code-mess, I was just prototyping ;-)

function getDaysOff( data, callback )
{
    Member.find({}, function( err, docs ) {
        if ( err )
        {
            console.error( err );
            return [];
        }
        console.log( "found " + docs.length + " team members" );
        docs.forEach( function( element ) {
            // reset all arrays befor continuing
            element.days_of_absence = [];
        } );
        data.forEach( function( element ) {
            for ( let i = 0; i < element.length; ++i )
            {
                var member = element[i];
                for ( let j = 0; j < docs.length; ++j )
                {   
                    if ( member.name.match( new RegExp( docs[j].name, 'g' ) ) )
                    {
                        console.log( member.name + " is " + docs[j].name );
                        for ( let k = 0;  k < member.absent.length; ++k )
                        {
                            docs[j].days_of_absence.push( member.absent[k] );
                            console.log( JSON.stringify( member.absent[k] ) );
                        }
                        console.log( JSON.stringify( docs[j].days_of_absence ) );
                        break;
                    }
                }
            }
        } );
        docs.forEach( function( element ) {
            element.save();
        } );
        callback( docs );
    });
}

And here is the Member schema:

var mongoose = require('mongoose')  
var MemberSchema = new mongoose.Schema(
    {
            _id: {
                        type: 'ObjectId'
                    },
            name: {
                        type: 'String'
                    },
            prename: {
                        type: 'String'
                    },
            days_of_absence: {
                        type: 'Array'
                    }
    }
);
module.exports =  mongoose.model('Member', MemberSchema, 'members');

When printing days_of_absence it yields something like this:

[
  [ { "date": "2018-01-28T23:00:00.000Z", "reason": "P" } ],
  [ { "date": "2018-01-29T23:00:00.000Z", "reason": "P" } ],
  ...
  [ { "date": "2018-09-27T22:00:00.000Z", "reason": "P" } ]
]

Where members.absent[k] is equal to the objects inside the inner array. (I already checked that). However I have no clue where the arrays around the objects come from. What am I missing? What I want is some like this:

[
  { "date": "2018-01-28T23:00:00.000Z", "reason": "P" },
  { "date": "2018-01-29T23:00:00.000Z", "reason": "P" },
  ...
  { "date": "2018-09-27T22:00:00.000Z", "reason": "P" }
]

UPDATE

As suggested I already tested if member.absent[k] is an array however printing it in the loop revealed that it isn't. console.log( member.absent[k] ) yields the desired:

{"date":"2018-09-02T22:00:00.000Z","reason":"P"}