Ion-select changes width depending of the value selected

Hi all,
I have the following code. A row with 2 columns, in the 1st column I have a ion-select, in the 2nd I have a button. The columns have width 60% and 40%. At runtime if I choose a value in the ion-select, the width changes. How I can avoid this behavior?
(You can see a screenshot at the end of the post)

      <ion-col width-60>
            <ion-select  [(ngModel)]="value" cancelText="Cancel" okText="Okay!">
              <ion-option *ngFor="let wtv of wt.getAttrValues()" [value]="wtv.value">{{wtv.value}}</ion-option>
      <ion-col width-40>
        <ion-item no-lines>
            <button ion-button block icon-left (click)="clickAddValue($event)" style="height: 60px;"><ion-icon name="add-circle"></ion-icon>Add</button>


width-60 and width-40 are not correct.

I used width-33 and width-60 and it works fine.

For the rigth columns width permitted see: