Walk Behind Lawn Mowers

I just purchased the 7021p walk behind mover and so far I love it!...well except for one slightly annoying feature on the collection bag. The bag has no stitching along the bottom/rear seam of the bag, which seems rather odd to me. Since I purchased it locally, I went back to the floor and looked at other (more sophisticated/expensive models) and all of their bag designs are fully enclosed (fully stitched around the bottom seam). I then asked the sales people (who are normally pretty knowledgeable about the products they sell) and they swore it was by design. But, in this case, they did not seem terribly confident about it. So, I would greatly appreciate a second opinion.

So, is this opening in the bottom/rear seam of my bag by design or is this a manufacturing defect? I have attached a picture of the area in question.

Otherwise, this is one of the nicest performing, ergonomically efficient mowers I've ever pushed (and I've pushed hundreds).

Many thanks in advance for your wisdom!
MG