patch 8.2.0833: mapping <C-bslash> doesn't work in the GUI Commit: https://github.com/vim/vim/commit/ca5bc746073b6fd4b7651bc02f7a18b1b43bd4ca Author: Bram Moolenaar <Bram@vim.org> Date: Wed May 27 22:08:34 2020 +0200 patch 8.2.0833: mapping <C-bslash> doesn't work in the GUI Problem: Mapping <C-bslash> doesn't work in the GUI. Solution: Reset seenModifyOtherKeys when starting the GUI. (closes https://github.com/vim/vim/issues/6150)

--- a/src/gui.c
+++ b/src/gui.c
@@ -803,6 +803,8 @@ gui_init(void)
 	if (!p_beval)
 	    gui_mch_disable_beval_area(balloonEval);
 #endif
+	// In case the terminal was used before ":gui".
+	seenModifyOtherKeys = FALSE;
 
 #if defined(FEAT_XIM) && defined(FEAT_GUI_GTK)
 	if (!im_xim_isvalid_imactivate())