linux ubuntu 16.04 (linux mint 18)
Unless i press shift the home key isn't moving the caret to the start of the line (as it should), or possible to the start of the line, excluding initial spaces and tabs.
The keybinding for Insertion Point to Beginning of Text on Line is Home by default, so that sounds odd. Are you using the default key map? Does the Home button work as it should in other applications? Please see the User Guide for how to add or change keybindings: