Found something really weird.
Writing a 'for' loop in vim, with #!/bin/bash as first line, so vim knows this is a script and turns on colour highlighting, brace matching etc.
# **********
count=0
for file in *.tif ; do
# an attempt at ocr'ing a page
let "count = count + 1"
done

but vim highlights the 'done' in red as being an error.
Removing *ONE* '"' from the 'let' line clears the 'error'...Huh?
So the 'error' is triggered above that point....

Changing the file extension from '*.tif' to '*.tiff' clears the error.

So, does anyone know *WHY* this happens? How/why does *vim* parse text for the file extensions? Is 'tif' a keyword for an extension? If so, what are the others?
I find this most intrigueing (although a work-around is easy!)

Adding to my post: it is NOT bash, it IS vim.

In a console:
for file in *.tif; do mv ${file} ${file}f ; done

works perfectly, with no flagged 'error'.

False alarm! Exceedingly opaque sleight of hand causes digression in the wrong direction.

It turns out to be one of the command switches in the ocr command which causes vim to choke

The command line is abbyyocr9 -if $count.tiff -f Text -of ../text/$count.txt

Vim burps on the 'if' in that command line. Bash does not. So I am using --inputFileName from here on.
Something to remember if things go wrong (pun intended).