I was just in Betheshee B-13, and stumbled upon a TyCorp that I couldn't see or target, but could still fire at me. Don't think I can repeat it, but if you have any questions, let me know.

One of my buddies have told me that he has encountered a few "invisible" Tycorps too, but this was in Rutilus I-7.

[edit typo (RelayeR)]

Related thread:
http://www.vendetta-online.com/x/msgboard/2/9507