History breaks when 2 instances of zathura are open
When zathura closes, it writes the history file as it was when it was opened plus the change to the opened file. So if A is opened and then B is opened and closed, the history of that B session will be discarded when A is closed because it was not there when A was opened. This should be fixable by reading the history file again before writing it, so any changes made since it was opened will be preserved.