On Apr 23, 5:46 pm, Richard J Kinch wrote:
Has anyone ever seen this problem before?

Yep. Overloading the machine, or loading stuff in after the water has
filled the tub, can cause items to walk over the top of the tub.

Thanks for all the input everyone! I inspected the tub a little more
carefully tonight, and there does appear to be a seam at the top
through which a sock could have escaped into the outer tub and down
into the pump. Lesson learned.