bug in substitute.txt functionality?

i have come across a weird phenomenon in using substitute.txt (within the experiment folder) to modify error messages, alerts and the like: the first entry of the substitute.txt appears to be ignored, while the subsequent messages are replaced as intended. this happens independently of the specific message number.
as a work around i ended up inserting another message that i won't need to be modified in a specific experiment as the first line. the one not working then becomes the second entry and is then replaced as intended.
may this be a bug? i am using medialab 2010.2.19.