Charactermancer supports feat choice, but Charactermancer+Level Up does not. The official stance is that it is officially an optional rule, and that the number of "hooks" a feat contains are not currently supportable (changes to skills, abilities, mods, proficiencies, etc.). This still doesn't explain why you can choose one at character creation but not at level up. The current workflow is to ignore the ASI (the final tab won't flag it as an error) and then use compendium drag and drop to pull the feat onto your character. Again, it only writes in the text of the feat, it's up to the player to make the changes to the sheet that feat would grant.