Bug description: The giant lair doesn't add giants to the party when you win, although the "Wun Wun added to the party" does appear.
How to reproduce it/when/why it happens: Just complete the giant's cave.
Your computer specs: Unknown precisely but all beyond M&BW's recommended.
Game version (and steam or downloaded): Up to date, Steam.
EDIT: They don't join battles or appear in the party menu, but they are in the character and companions overview