Debian /etc/cron.d/ gotcha

I typically use /etc/cron.d to store all of my system crontabs. I recently ran into an issue that I had either not run into before, or fixed and paid no attention to. Files stored in /etc/cron.d/ or any /etc/cron.* directory need to adhear to the run-parts Debian cron script namespace which consists is

(^[a-z0-9][a-z0-9-]*$)

for the regex impared this does not include the dot character. If you have a file in /etc/cron.d/ that has a dot in it it will not be evaluated by cron. I have seen mention of underscore not being valid but in my testing underscore was not an issue, only dots.