The MacOsX Windowing environment provides features and related keyboard sequences ( Cmd-`) to switch between open windows in the context of an application i.e. open Libreoffice files in this case. There is no Libreoffice system macro collecting this sequence and thus inserting wrong characters in the file displayed eventhough the window switch takes place. Related to French keyboard only ?
Thanks for your bug report. It happens in the Spanish keyboard layout as well… *** This bug has been marked as a duplicate of bug 53965 ***