Like the title says, I have created a new Grease Pencil Object (GPencil), went into the Draw Mode (upper left menu), than pressed C, but I can't exit from this feature (pressing ESC or anything else doesn't seem to help).
To be precise: pressing C in draw mode constrains the drawing into a circular/radial guide.
Possibly a bug? Thanks G
EDIT SOLUTION: Check the box in the upper viewport, with other guides checkboxes (Circular, Radial, Parallel...)