Could not getting feedback on design be more helpful than getting feedback?

Could it be that if one received no feedback for a design, the final design could be better than if the designer had received feedback? Can feedback simply "validate" the current idea and not prompt improvements?

The study in short (more details in our paper "The Effect of Prototyping and Critical Feedback on Fixation in Engineering Design"at CogSci'11 in Boston in July):
29 student participants were asked to design a device to move balls from one box to another. The design prompt included some detailed requirements about how the design should of should not be such as that the balls can not be damaged. The participants were guided through a design process consisting of the following steps: idea generation, concept refinement, and final build. The students showed their designs after each step to a reviewer. The participants were divided into three groups: group 1 received a standard technical feedback typical to engineering education, group 2 received a crit style feedback typical in arts, and group 3 only showed their designs to the reviewer but received no feedback.

Results:
At this initial stage we observed the changes (improvements) made to designs after each feedback session. While we found some expected results such as the technical feedback group (1) was most likely to not change their design if there was no design requirement violation, we also find that the no feed back group (group 3) was most likely to change their concept of even come up with a totally new concept than the other two groups. This was highly surprising. Further work is needed to investigate why this happened. Could it be that seeing your design being reviewed but not hearing if it needed improvements was the best motivator to improve the design on your own?