I'm sure lines with errors used to be highlighted in some way. Not seeing this now. Of course it could always been a figment of my imagination anyway! :)

The red error markers do not appear if there is a 'lib_' file present. I have a test script that does not use anything in my 'lib_' file. If I rename the 'lib_' to 'xlib_' (the actual name is 'lib_AP') then the red markers will appear.