The bug was present in the “Reject Cross-Domain Cookies” feature of KDE Libraries. Thiago Macieira noted in the KDE Libraries Revision 974b14b8 that he observed that his web cookies were being forgotten following a kded restart. Macieira observed that “mCrossDomain member variable in the cookies” had a value of 127 and mCrossDomain being a Boolean this value doesn’t make any sense at all.
"For several months now, all my cookies would be forgotten after a kded restart. After debugging the problem, turns out that mCrossDomain was of value 127, which makes no sense for a boolean", Macieira writes in the revision notes.
The issue was present within KDE's KCookieJar within the HTTP KIOSlave of kdelibs. "This variable has been present since 2002, which means that the "reject cross domain cookies" feature has been broken for 10 years and 8 months", adds Macieira.