Strange bug with "git log" - pdftotext?

I'm trying to search my git log history for a particular term - 
"unobtrusive" - so I run this command:

git log -S unobtrusive --oneline

When I do this, this is displayed and I'm in an interactive less 
terminal or something:

pdftotext version 4.00
Copyright 1996-2017 Glyph & Cog, LLC
Usage: pdftotext [options] <PDF-file> [<text-file>]
  -f <int>             : first page to convert
  -l <int>             : last page to convert
  -layout              : maintain original physical layout
  -simple              : simple one-column page layout
  -table               : similar to -layout, but optimized for tables
  -lineprinter         : use strict fixed-pitch/height layout
  -raw                 : keep strings in content stream order
  -fixed <number>      : assume fixed-pitch (or tabular) text
  -linespacing <number>: fixed line spacing for LinePrinter mode
  -clip                : separate clipped text
  -nodiag              : discard diagonal text
  -enc <string>        : output text encoding name
  -eol <string>        : output end-of-line convention (unix, dos, or mac)
  -nopgbrk             : don't insert page breaks between pages
  -bom                 : insert a Unicode BOM at the start of the text 
file
  -opw <string>        : owner password (for encrypted files)
  -upw <string>        : user password (for encrypted files)
  -q                   : don't print any messages or errors
  -cfg <string>        : configuration file to use in place of .xpdfrc
  -v                   : print copyright and version info
:

When I hit the down arrow, it scrolls down, repeating this output 
infinitely until I hit 'q'.  What is going on here??

-- 
Best regards,
Jeremy Morton (Jez)