It seems if you use double quotes (" ") then it truncates very weirdly indeed, however if you use single quotes (' ') it works for both TEXT and VARCHAR(255).
e.g. This works: Credit or Debit Card <img src='images/square-400.jpg' style='max-width: 100%'>
Ok, I see the problem then and what's happening is it is truncating on the quotes. I've fixed this now and added to the fix to the file... vsadmin/inc/incpayprov.php ...in the updater. For ASP users too this is done in incpayprov.asp