How do I turn off Ctrl+Up/Down switching tabs?

[SotiCoto]

I should probably just get Excel or something like it... but I've been trying to use Google Sheets.
The problem arose because Google Sheets, much like Excel before it, uses Ctrl+Up and Ctrl+Down to move to the top or base of the current block of populated or unpopulated cells respectively.
Avant, on the other hand, has entirely different ideas... and when I press Ctrl+Up to get back to the top of the spreadsheet, Avant switches tabs.


How do I stop it doing that? I couldn't find anything for it in the options and it is particularly annoying (it doesn't even make sense. Ctrl+Left/Right I could understand, but Up/Down is nonsense).