Disappearing convoy

Just ran into a strange bug... I ran into a small convoy consisting of one Bogue (I think) carrier escort and four destroyers. I was observing via the attach periscope when the convoy simply disappeared. This was in DJ15 on 9/10/1943 at 6:26 am.

So I reloaded an older save, and manouvered into position, and then using the external view, watched the entire convoy simply vanish. All in all, pretty annoying