Under TYPO3 8 LTS and Development-context the parser should generate a new file if include-files where changed. This worked in TYPO3 7 LTS (maybe a unknown effect because i think the commit https://github.com/kaystrobach/TYPO3.dyncss/pull/39 breaks this behaviour on LTS 7 too).
Currently I added an additional Development-Mode check in Classes/Parser/AbstractParser.php:289 to disable caching.
if (@filemtime($outputFilename) < @filemtime($inputFilename) || $this->_checkIfCompileNeeded($inputFilename) || ApplicationContext::isDevelopmentModeActive()) {