Identical in nature to
MDL-19112 as noted by Eloy
It seems that the "choosecoursefileorimsrepo" formslib group element doesn't allow to specify any attribute in the $attributes parameter. They are set to the group element without effect in the text field. So things like size or maxlength cannot be specified.
As the group only has 2 elements (buttton and text), make it to forward any attribute received straight to the text element.