If a module breaks your site after a simple 'save', you are most likely using the extension 'Advanced Module Manager'.
The 'Advanced Module Manager' replaces the tags's condition with its own and raises a compatibility issue.
Luckily, there are 2 possible workarounds until I accommodate my extensions to work with Advanced Module Manager.

The workarounds:

• run the module outside 'Advanced Module Manager',
• select a tag, save the module, unselect the tag, save again.

To run outside the Advanced Module Manager, replace the URL of the modules list page from
option=com_advancedmodules&view=module
to
option=com_modules&view=module
or disable that extension all-together while you make changes to the modules.