Core deletes callbacks from inexistent variables

[00007fdb03528fa8] core input error: cannot delete callback 0x1035f60e0 from nonexistent variable 'next-title'
[00007fdb03528fa8] core input error: cannot delete callback 0x1035f60e0 from nonexistent variable 'prev-title'
[00007fdb03528fa8] core input error: cannot delete callback 0x1035f60e0 from nonexistent variable 'menu-popup'
[00007fdb03528fa8] core input error: cannot delete callback 0x1035f60e0 from nonexistent variable 'menu-title'
[00007fdb03528fa8] core input error: cannot delete callback 0x1035f6430 from nonexistent variable 'next-chapter'
[00007fdb03528fa8] core input error: cannot delete callback 0x1035f6430 from nonexistent variable 'prev-chapter'

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