TYPO3 Core

The documentation allow lowerCamelCase for actionnames within the controller.
https://docs.typo3.org/typo3cms/ExtbaseGuide/singlehtml/ (last visit 2016-08-27-19:30)
"_.... allowed Actions are registered in ext_localconf.php and thenceforth only referenced by name. For example, list, show, detail, update, edit, delete. These names are also used within the page Uri. Within the ActionController, a lowerCamelCase name is required for every action: for example, the action list refers to the method listAction: ...._

The Function getControllerActionName in extbase\Classes\Mvc\Request.php tests not with lcfirst for lowerCamelCase. It tests for general lowercase with strtolower.

    public function getControllerActionName()
    {
        $controllerObjectName = $this->getControllerObjectName();
        if ($controllerObjectName !== '' && $this->controllerActionName === strtolower($this->controllerActionName)) {
            $actionMethodName = $this->controllerActionName . 'Action';
            $classMethods = get_class_methods($controllerObjectName);
            if (is_array($classMethods)) {
                foreach ($classMethods as $existingMethodName) {
                    if (strtolower($existingMethodName) === strtolower($actionMethodName)) {
                        $this->controllerActionName = substr($existingMethodName, 0, -6);
                        break;
                    }
                }
            }
        }
        return $this->controllerActionName;
    }

current work around:
Use only one-name-actions with no upper-case-character

The usage of 'lcfirst' instead of 'strtoLower' would allow a lowerCaseWriting. You must extend although the allcocation of $this->controllerActionName to prevent error because of misspelling (untested version)

    public function getControllerActionName()
    {
        $controllerObjectName = $this->getControllerObjectName();
        if ($controllerObjectName !== '' && $this->controllerActionName === lcfirst($this->controllerActionName)) {
            $actionMethodName = $this->controllerActionName . 'Action';
            $classMethods = get_class_methods($controllerObjectName);
            if (is_array($classMethods)) {
                foreach ($classMethods as $existingMethodName) {
                    if (lcfirst($existingMethodName) === lcfirst($actionMethodName)) {
                        $this->controllerActionName = lcfirst(substr($existingMethodName, 0, -6));
                        break;
                    }
                }
            }
        }
        return $this->controllerActionName;
    }

I Think, the better way would be to throw an exception to announce the misconfiguration.
untested version

    /**
     * Returns the name of the action the controller is supposed to execute.
     *
     * @throws Exception\InvalidArgumentNameException
     * @return string Action name
     * @api
     */
    public function getControllerActionName()
    {
        $controllerObjectName = $this->getControllerObjectName();
        if ($controllerObjectName !== '')  {
            if ($this->controllerActionName === lcfirst($this->controllerActionName)) {
                throw new \TYPO3\CMS\Extbase\Mvc\Exception\InvalidArgumentNameException('No lowerCamelCase for action in request or configuration.', 58976458767);
            }

            $actionMethodName = $this->controllerActionName . 'Action';
            $classMethods = get_class_methods($controllerObjectName);
            if (is_array($classMethods)) {
                foreach ($classMethods as $existingMethodName) {
                    if ($existingMethodName === lcfirst($existingMethodName)) {
                        throw new \TYPO3\CMS\Extbase\Mvc\Exception\InvalidArgumentNameException('No lowerCamelCase for action in request or configuration.', 58976458767);
                    }
                    if ($existingMethodName === $actionMethodName) {
                        $this->controllerActionName = substr($existingMethodName, 0, -6);
                        break;
                    }
                }
            }
        }
        return $this->controllerActionName;
    }