When you receive a support request for a your product that extend another product.

After few emails you get the access on the website and you discover that is using an old version of the software that you extend and that your support is crappy on that.

Never forget to ask before everything the version of stuff to save time.
Also don't hesitate to give a reimburse for this case or suggest for an update so you can sleep better and maybe ADD AN ALERT FOR THE OLD VERSION THAT YOU FORGOT TO DO on your release.