When attempting to add more than 26 conditions using custom expression, after clicking update, the action does not save correctly and you get error:

Undefined offset: 971 [actionconf.php:402 ? CFrontendApiWrapper->get() ? CApiWrapper->__call() ? CFrontendApiWrapper->callMethod() ? CApiWrapper->callMethod() ? CFrontendApiWrapper->callClientMethod() ? CLocalApiClient->callMethod() ? call_user_func_array() ? CAction->get() ? CAction->addRelatedObjects() in /usr/share/zabbix/include/classes/api/services/CAction.php:1541]

Then, once you go back in, you see 2 A's and are unable to make any further changes, except to delete both A's.

See attachment