In the companions overview screen, the xp to next level shown is only correct up to level 30. Once a companion reaches level 30, it shows a negative amount (- current xp) needed for level 31, as if the list of xp needed for the next level stopped at 30.
When going to the individual screen of a companion from the companions overview screen, the weapon proficiencies are shown as shifted one position down, i.e. one-handed weapons is empty, two-handed weapons has the value of one-handed weapons, etc.
Siwi is shown as having Searoburh as origin, but offers to go to Dorce Ceaster when asked to contact his connections.
Mihael ap Cadwalladr is shown as having Licidfelth as origin, but offers to go to Caer Luit Coyt when asked to contact his connections.