A while back I sent a message complaining about an irritating mark that quanta puts in whenever there's a space at the end of the line.  Then, though I found a way to solve the problem, the quanta mail server wound up dutifully blocking my incoming emails, to prevent spam, and I've been too busy until now to configure a mail account to conform to its demands. 
 
Anyway, in case the same thing is annoying anyone else I figured out how to fix it -- it's actually a KDE problem in general, and Kate does the same thing unless you dig through some inconvenient menus to shut it off.
 
Here's how:
 
  Settings >> configure editor >> Editing (icon) >>
    show tabs (checkbox)
 
Uncheck it to get rid of the annoying marks.  Nowhere does it explain why a space is considered to be a "tab" for the purposes of the checkbox.
 
I hope this may help somebody else who is having the same problem.
 
  -= miles =-