1. Actually this should be already fixed in the last dev. release. Can you try it out?
Alternatively you could do the following modifications:
Go to \components\com_comment\templates\default\default_form.php
line 155 looks like this:
<button class="btn-link btn-small ccomment-posting-as">{{user.getDefaultName}}</button>
add type="button" to it like this:
<button type="button" class="btn-link btn-small ccomment-posting-as">{{user.getDefaultName}}</button>
Then you need to do the same for the cancel button on line 250:
<button class="btn ccomment-cancel"><?php echo JText::_('COM_COMMENT_CANCEL'); ?></button>
change it to
<button type="button" class="btn ccomment-cancel"><?php echo JText::_('COM_COMMENT_CANCEL'); ?></button>
Cheers,
Daniel