As you can see below, PhantomWolf has had it happen to him under conditions that aren't defined by the current warning; Multicannon are definitely NOT "Unique" by Frontiers definitions, you can have more than one on a ship.
That it doesn't trigger when others move shields about doesn't mean my speculation (which is all it was) is inaccurate; it just means there's other factors involved too. My point is that if you follow Frontiers warning, which I did, you can STILL brick your account because there's a wider set of triggers than they understood and warned you about. The risks for falling into an unknown case are extremely high. So why take them?
Hence don't play with storage for now. Really, don't. The shield I may end up losing was Prismatic, and Grade 5 engineered. That's literally months of gameplay to get back again, as I dropped powerplay instantly after getting a Prismatic for my trading ships.
Not suggesting for a moment that you are wrong to urge caution, but as I posted on your own thread regarding this, I have used module storage / transfer just fine with no problems. Here's what I did:
1. Stored my Asp's (engineered) C5 shield gen so I could buy and upgrade a higher class C5 for my FDL.
2. Removed C4 shield gens from Cobra Mk III and Viper IV, stored them. Both had existing engineer mods.
3. Flew in Asp to Khun and transferred both C4 shield gens to Khun.
4. Engineered new C5 shield gen in Asp, stored it.
5. Transferred first C4 shield gen to Asp, re-engineered it. Stored it.
6. Transferred second C4 shield gen to Asp, re-engineered it. Stored it.
7. Transferred previously engineered C5 shield gen back to Asp. Flew back to home base. Transferred both C4 shield gens back from Khun to home base. Stored C5 engineered shield gen.
8. Stored C3 shield gen (previously engineered) from Imp Courier. Transferred it to Asp. Flew to Khun, and re-engineered C3 shield gen. Flew back to home base, stored shield gen and transferred it back to Imp Courier.
9. Transferred C4 shield gens back to their respective ships.
10. Transferred C5 shield gen from storage to FDL.
11. Transferred original C5 shield gen back to Asp.
Five ship's shield generators successfully stored, transferred and upgraded then re-installed in the correct ship. No issues, even logged out to main menu and back in to check that it was all working. I did all this messing around because the Asp was only 6 jumps to Khun, and other ships would have been from 10 to 20.
So while clearly you have had an issue, it would seem it is not universal.
As I said, good of you to urge caution.

But to those suggesting that module storage / transfer is totally broken, I'd have to say it doesn't look that way to me.