Created by: zalog
Because of css specificity textarea won't reset to height: auto when the parent is .form-group-sm or .form-group-lg. Please take a look here: http://www.bootply.com/nuSb245tba
I hope this helps. You can close #15592
Also we have to keep in mind that this mixin output this: line 81: textarea& become: textarea.form-group-lg .form-control and it's not fine :)
Thanks!