Steps to reproduce the issue

Create a form with a modal category field

<field
name="category"
type="modal_category"
label="category"
labelclass="control-label"
edit="false"
addfieldpath="/administrator/components/com_contact/models/fields"
/>

Expected result

When you click on the select button the modal popup should open

Actual result

When you click on the select button nothing happens

System information (as much as possible)

Additional comments

Bug fix: /administrator/components/com_categories/models/fields/modal/category.php

149:        // Edit category button
150:        if ($allowEdit)
151:        {
152:            $html[] = '<a'
153:                . ' class="btn hasTooltip' . ($value ? '' : ' hidden') . '"'
154:                . ' href="index.php?option=com_categories&layout=modal&tmpl=component&task=category.edit&id=' . $value . '"'
155:                . ' target="_blank"'
156:                . ' title="' . JHtml::tooltipText('COM_CATEGORIES_EDIT_CATEGORY') . '" >'
157:                . '<span class="icon-edit"></span>' . JText::_('JACTION_EDIT')
158:                . '</a>';
159:
160:            $html[] = JHtml::_(
161:                'bootstrap.renderModal',
162:                'modalCategory-' . $this->id,
163:                array(
164:                    'url' => $link . '&' . JSession::getFormToken() . '=1"',
165:                    'title' => JText::_('COM_CATEGORIES_SELECT_A_CATEGORY'),
166:                    'width' => '800px',
167:                    'height' => '300px',
168:                    'footer' => '<button class="btn" data-dismiss="modal" aria-hidden="true">'
169:                        . JText::_("JLIB_HTML_BEHAVIOR_CLOSE") . '</button>'
170:                )
171:            );
172:        }

149:        // Edit category button
150:        if ($allowEdit)
151:        {
152:            $html[] = '<a'
153:                . ' class="btn hasTooltip' . ($value ? '' : ' hidden') . '"'
154:                . ' href="index.php?option=com_categories&layout=modal&tmpl=component&task=category.edit&id=' . $value . '"'
155:                . ' target="_blank"'
156:                . ' title="' . JHtml::tooltipText('COM_CATEGORIES_EDIT_CATEGORY') . '" >'
157:                . '<span class="icon-edit"></span>' . JText::_('JACTION_EDIT')
158:                . '</a>';
159:        }
160:
161:        $html[] = JHtml::_(
162:            'bootstrap.renderModal',
163:            'modalCategory-' . $this->id,
164:            array(
165:                'url' => $link . '&' . JSession::getFormToken() . '=1"',
166:                'title' => JText::_('COM_CATEGORIES_SELECT_A_CATEGORY'),
167:                'width' => '800px',
168:                'height' => '300px',
169:                'footer' => '<button class="btn" data-dismiss="modal" aria-hidden="true">'
170:                    . JText::_("JLIB_HTML_BEHAVIOR_CLOSE") . '</button>'
171:            )
172:        );