Removing an extension which is highly dependend on other extensions (like subsubsubinheritances of themes) takes some time
Having installed: themes, gridelements > themes_gridelements > theme_boostrap > ...
To uninstall gridelements you have to manually remove all dependend extensions in reverse order.
After questioning the admin the extension manager could uninstall a whole extension tree.
The other way round already works: The extension manager installs required extensions.
TYPO3 CMS 6.2.17 + 7.6.2