Has anyone addressed this broken feature

Why on earth would you pick speed to calibrate? 

Probably cause he has two 4's that they wants rolled into 5 or 6's... 

It does suck when it rolls negative or 0, but it would be a broken system if it only got better. Everyone would have god mods and it wouldn't be a fun time.

But why not choose Crit Chance or Offence, that could result in an additional 3,4,5 or 6 speed instead of the very slim possibility of an additional 1 speed?

If OP wants the mod to have better speed secondaries, they’ve gone for the option that has the lowest odds of success and the lowest impact if they are successful. 

I totally agree with your point though - if the reroll only ever gave an improvement that would be more broken than it currently is. 

I definitely agree they should have finished slicing it first before calibrating, cart before the horse situation for sure. Just giving an answer on your question though 😉 

That still doesn’t explain it (to me, anyway).

Calibrating before you finish slicing a mod is absolutely fine and I’ve done that dozens of times myself. I don’t think opting to calibrate this mod was a bad decision. 

But when you’ve got a mod with 4 speed hits, choosing to calibrate speed hoping for an improvement is madness.

It looks to me like that mod has had +6 (x2), +5 and +4 to get to +21 overall. So by choosing speed as the secondary for calibration, OP has 25% chance of rolling speed and then a further 50% chance of choosing one the 2 rolls that have any prospect of being improved, and then further RNG as to whether or not the new roll is actually any better than the current stat. 

In fact, I think it’s a triumph of RNG that the roll was the same speed. The odds of a decrease were higher. 

That's working as intended.  Any stat can be raised and if the same stat hits, it can go up or down.  There are actual broken features they need to fix.

You're just wasting materials trying to upgrade that speed to have more speed.