Is it possible that one of your rakes attempts to seed streamtraces outside of the fluid domain? This might explain what you are seeing, although I don't know whether you are seeding these streamtraces interactively or through a macro.
On the whole, this sounds like an issue which should be sent to Tecplot support (support at tecplot dot com). It is best if you can send along a layout/macro and data file which easily illustrate the problem. They will be able to help determine if this is actually a bug or if there is a reasonable explanation for this behavior.