I have had the very same problem on OpenServer 5.0.5/RS505A and never found a satisfactory solution. I contacted SCO support about it as well, but they were unable to reproduce the problem (of course), and the problem went away at my end. I've seen it on-and-off... sometimes switching the root shell from Korn shell to Bourne shell (sh) stopped it happening, but I've seen it under both shells.
Annihilannic.