What application are you using to create the text?
Some applications (e.g. Word) treat certain repeated character combinations as 'shortcuts' to special characters; for example three '.' characters is turned into an ellipsis character.
I don't know if Word does something similar with '-' characters; if it does, perhaps the replacing character is not within the selected printer font, and thus either a space, or nothing, is printed.
Try doing a print to file and examine this to see just what character(s) are present in the output.