I have created D&D 5e Ranger, Sorcerer and Warlock characters in PCGen 6.06.01 and 6.08.00 RC2
using the D&D 5e System Reference Document 5.1 data set
and found the same bug affecting each character generation.
The "Spells Known" does not allow lower level spells to be added or swaped
despite there being higher level spell slots available.
The error generated is "You can only learn 0 spells for level 1 and there are no higher level spots available."