If using a media field type within a repeatable subform there is an issue with the background overlay of the media lightbox once the number of new subforms extends beyond the viewport. The background overlay of the media field lightbox does not extend to the full height of the screen

Subform code example...

<?xml version="1.0" encoding="UTF-8"?>
<form>
    <fieldset name="images" class="image-subform">
        <field name="j51_image" type="media" default="" label="MOD_J51_IMAGE"  description="MOD_J51_IMAGE_DESC" size="30" />
        <field name="j51_text" type="textarea" filter="raw" rows="4" cols="42" default="" label="MOD_J51_IMAGETEXT" description="MOD_J51_IMAGETEXT_DESC" />
    </fieldset>
</form>

1. Continue to add subforms until the page height is increased
2. Click 'Select' on the media field of the last subform

Result

Backgound overlay does not extend to the full height of the screen.

System information

Joomla 3.6.2