Not poor design, the Feather System has to be unlocked at some point. And testing it early, at Mach 1.4 might be a really good idea before you (I assume) commit to needing it.
And there's a good possibility removing its contribution to the center of pressure too early is what caused the destruction.
Hard to say if poor design is a contributing factor or not - if the release mechanism is easily confused because it's a tiny little switch that looks just like all the other tiny little switches, then yeah, it may be poor design. In new endeavors, especially the often unforgiving aviation arena, frequent and focused training often makes up for poor design, or less-than-wonderful human factors engineering, or other recognized-after-the-event shortcomings - until it doesn't.
I would assume that in typical aircraft cockpit, most of the prominently placed tiny little switches are actually important and unimportant tiny little switches are the exception.
And there's a good possibility removing its contribution to the center of pressure too early is what caused the destruction.