Actually, rather than a feature, you are seeing a "minor" AI bug that we haven't gotten to eliminating yet (but will for LWAMI4).
The AI actually runs aground in several instances... in most cases, it's not beneficial to the AI, but as you saw, sometimes it can be.
I could comment on how this or that needs to be changed, but we are probably going to wind up completely redoing all the AI evasion code (at least for submarines) for the new torpedo controls and behavior, so I'll just say for now that, "we are looking into this."
I hope you are enjoying LWAMI, 688iG.
Cheers,
David