I’ve found a bug in the 1.4.0-EPA1 regarding the dhcp-options vendor-class-id validation.
The regex used to validate the entry doesn’t take the string if it contains dot, which can be required by some ISP as mine.
I've just added a dot in the first regex to make it work on my installation, but I'm not used to them so I'm not sure if it was the proper way to do it.