Yes, if one of the provinces is owned, even if not controlled, province will be ceded. Very frustrating for the controller if not at war against the new owner.
Do you have a savefile with such situation before the date of the event?
i only have this which i kept in another format
name = "December 20, 1424 : Foix is now granting Brabant military access to their country."
name = "January 1, 1425 : Richard II rose to the throne in Ulster."
name = "January 1, 1425 : Blanka I.a rose to the throne in Navarre."
name = "January 1, 1425 : Baraq rose to the throne in Golden Horde."
name = "January 2, 1425 : §YCyprus had The Piracy from Cyprus."
name = "January 6, 1425 : §YLuxemburg had Death of Jan the Merciless."
name = "January 7, 1425 : §YHungary went with §WGrant Straubing to Habsburg§Y in Death of Johann of Bavaria-Straubing."
name = "January 7, 1425 : §YAustria went with §WAccept Straubing and fight for it§Y in Bavaria-Straubing is granted to "
name = "Habsburg."
name = "January 7, 1425 : §YBavaria went with §WOppose the Habsburgs and Sigismund§Y in Bavaria-Straubing is granted to "
name = "Habsburg."
name = "January 12, 1425 : Poland entered a Royal Marriage with Moldavia."
name = "January 16, 1425 : §YMilan went with §WWe have lost confidence on him§Y in Carmagnola's Threat."
name = "January 26, 1425 : §YVenice went with §WAccept Carmagnola's Offer§Y in Carmagnola."
name = "January 30, 1425 : §YStyria had Change of regent."
name = "January 30, 1425 : Hermann II von Cilli rose to the throne in Styria."
name = "February 1, 1425 : §YSerbia had Stefan Lazarevic."
name = "February 7, 1425 : Vasily II rose to the throne in Muscovy."
name = "February 13, 1425 : Luxemburg accepted peace with Brabant on the following terms: Full Annexation of "
name = "Luxemburg by Brabant."
................................................
while a normal file for this indicates which choices LUX made
name = "November 11, 1424 : Luxemburg entered a Military Alliance with Burgundy and Brabant."
name = "January 1, 1425 : Blanka I.a rose to the throne in Navarre."
name = "January 1, 1425 : Richard II rose to the throne in Ulster."
name = "January 2, 1425 : §YCyprus had The Piracy from Cyprus."
name = "January 6, 1425 : §YLuxemburg went with §WHonour the agreement with Burgundy§Y in Death of Jan the Merciless."
name = "January 6, 1425 : §YBurgundy had The Dutch Wittelsbach possessions."
name = "January 7, 1425 : §YHungary went with §WGrant Straubing to the Bavarian Wittelsbachs§Y in Death of Johann of "
name = "Bavaria-Straubing."
name = "January 7, 1425 : §YBavaria had Inheritance of Bavaria-Straubing."
name = "January 16, 1425 : §YMilan went with §WWe have lost confidence on him§Y in Carmagnola's Threat."
name = "January 23, 1425 : §YStyria had Change of regent."
name = "January 23, 1425 : Hermann II von Cilli rose to the throne in Styria."
name = "January 26, 1425 : §YVenice went with §WAccept Carmagnola's Offer§Y in Carmagnola."
name = "February 7, 1425 : Vasily II rose to the throne in Muscovy."
..........................
so the bottom ( current game) indicates which choice LUX made , while the top "notes" said the event fired , but no choice was made
maybe as the top notes indicated, LUX was annexed in a month by HAU