What are the justification settings? Looks like justified with last line aligned left, and that would allow ID to change the spacing.
Thanks, that appears to be the issue. I'm not familiar with this justification. I'm used to left, center, and right. I still don't understand what this is doing, but changing it to left solves the issue.
When you sel3ect one of the Justified settings you are telling InDesign to adjust spacing and/or glyph width within your chosen parameters in order to fill the width of the column. With a fixed-width font like courier you would most likely not want to use justified text and should stick to left-aligned.
In addition to what Peter says, you probably should also disable ligatures. This is by default enabled in InDesign, and as you can see, the combo "fl" in "flow" is replaced by a single, one-character wide, combo "fl".
The 'other' common ligature is "fi" but that doesn't seem to occur in this short fragment. Courier is an old fashioned font and not likely to contain more ligatures than these two.