Unix utilities often read in the entrie file, then process it, eg., sort, gcc.
The old presumption was that the file was truncated or corrupted- this used to happen a lot when disks went bad on a monthly basis 25 years ago. The EOF marker for a text file is ASCII 26. So if one bit of a real byte got twiddled, an EOF could appear where it was not supposed to be.
That's the origin of the warning.