To reproduce, change Next Tab and Previous Tab to Ctrl+PageDown and Ctrl+PageUp, resp. The next time you open Kate, a dialogue opens: "Ambiguous Shortcuts: There are two actions (Previous Tab, Previous Tab) that want to use the same shortcut (Ctrl+PageUp). This is most probably a bug. Please report it in bugs.kde.og" A second dialogue opens after the first with the same text, mentioning Next Tab. Ctrl+PageDown/Up do not work for these functions despite the fact that they appear correctly, as set, in the Configure Shortcuts dialogue. When hitting Ctrl+PageUp, for instance, a dialogue appears: "Ambiguous shortcut detected: The key sequence 'Ctrl+PgUp' is ambiguous. Use 'Configure Shortcuts' from the 'Settings' menu to solve the ambiguity. No action will be triggered."
*** This bug has been marked as a duplicate of bug 383721 ***