When focus on editor, Ctrl+Tab or Ctrl+Shift+Tab doesn't switch tabs, instead, this combo moves focus from editor to next/prev control.
But If tab-notebook itself is focused, Ctrl+Tab and Ctrl+Shift+Tab works correctly. So, to switch between tabs, I need click on tab bar or hit Ctrl+Shift+Tab (which moves focus to tab bar) and only then I can use Ctrl(+Shift)+Tab to navigate between tabs. And after that I have to hit "Tab" to return focus back to editor or again use mouse.
Codeblocks 16.01, from Debian Stretch repository.
Tried install and uninstall contrib plugins, no results.
Desktop environment: MATE 1.14.1 (based on GNOME 3.20).
P.S. This ticket got 404th number, but I hope someone will find it. :)
I can reproduce this. Thank you for reporting.
As a workaround for now you can use the ctrl-, and use the stack based switching.