Enlighten me as to why the feathering of the tail would be more dangerous at mach 1 that at 1.4 ?
I think the information is either incomplete or someone has gathered a fact and reported it without understanding what it means.
My understanding is that the wing/tail feather mode is normally used only during re-entry and perhaps M 1.4 is the Mach number at which is is normally deployed. I don't really know, but that factoid might be inadvertently or incorrectly blended into the current news. Anyway, I imagine going into feather mode would most likely be at very high altitude with low dynamic pressure. In other words, the true speed, measure in either mach number or true airspeed, would be rather high but because the air is so "thin" the airframe wouldn't have a lot of load on it; i.e. indicated airspeed (dynamic pressure) would be low............ very low.
Contrast that with going into feather at 50,000 feet and Mach 1.0; i.e. shortly after release. Working from memory (you should look it up to get the real number) the indicated airspeed would be about 250 knots and that, I would imagine, is too fast to feather the wing/tail system. I have no idea how high they are when they go into "normal feather mode" during re-entry, but if it's up around 150000 feet, the indicated airspeed would be way down, perhaps 50 knots or so at M 1.4. Again, look up the real figures. My brain isn't what it used to be and high mach number flying as well as my university aerodynamics training are both now only a distant semi-memory.
Of course, depending on who you talk to about flying around on the fringes of "Space", the measurement of the speed of sound and the concept of indicated airspeed begin to unravel a little bit, but you get the idea. That is to say, M 1.4 at high altitudes might be perfectly safe for a major configuration change while doing so at M 1.0 at low altitudes would be a disaster. It has a great deal to do with the dynamic pressure (indicated airspeed to most folks).
I think we're victims of bad reporting and/or lack of aerodynamic understanding and/or ignorance of just what the flight profile is normally like.