Bug #2785590 shows that escaped single quote will break the syntax highlighting in SQL, which I recreated with ease in many scenarios.
Checking out the LexSQL.cxx, I found that there was a check for a variable "sqlBackslashEscapes," which I couldn't find set anywhere. Easy fix is to remove it and the bug is cleared (tested on 5.3.1). Maybe it isn't being set where it should be?
svn patch for bug 2785590
Fixed in Notepad++ but not in Scintilla.
Don