show_page_heading doesn't work for component "List of all tags" because of a small error in
components/com_tags/views/tags/tmpl/default.php at line 19:
<?php if ($this->state->get('show_page_heading')) : ?>
should be replaced by:
<?php if ($this->params->get('show_page_heading')) : ?>
System information (as much as possible)
Joomla! Version Joomla! 3.3.5 Stable [ Ember ] 30-September-2014 14:00 GMT
Joomla! Platform Version Joomla Platform 13.1.0 Stable [ Curiosity ] 24-Apr-2013 00:00 GMT
Additional comments
This issue is fixed in Joomla 3.4.1 with this PR #6274. So upgrade your site to latest version of Joomla and the issue will be gone.