O problema é que ctrl + c também é o atalho para copiar algo. Então você tem que ligar o atalho SIGKILL para outra coisa que o atalho no terminal funciona. Por exemplo, com AutoKey
Houve um ingresso no guake.org há três anos, resposta que explica bem:
Ctrl+C is historical key combination for killing foreground process in unix terminals. Under the hood, it sends SIGINT signal to the foreground process, and default effect of that is termination of the process. However, any application is able to catch and block that signal, ignoring the request for termination. Several dozens of other signals exist with their specific functions, SIGSTOP for example stopping the process (with possibility to resume later), SIGTERM unconditionally terminating the process, etc.
But, Ctrl+C is also widely known shortcut to "copying" operation, ubiquitously used in MS Windows applications. Modern Linux desktop environments emulate the behavior to cause less confusion to migrated users, but the native selection system of X windows uses middle mouse button for "copypasting" rather then hotkeys. Just select source text and click with the third button in the destination area. Selected text will be pasted.
As Guake uses VTE component provided with GNOME (which is the one responsible for handling ^C, the terminal killing one), I'm afraid, we cannot help the conflict. Bind "copypasting" Ctrl+C to something other (I have it binded to Ctrl+Shift+C) and get used to it; or try to accommodate yourself with the middle click way - it's pretty convenient indeed. And yeah, patches are as always welcome - so you may try to fix everything yourself (though this is not a bug, this is a conflict: nothing to fix, rather to find not-very-harmful workaround).
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