String changing mystery on Ibanez EHB

[Spingere]

I recently changed the strings on my lovely Ibanez EHB 1265ms.

 

I put in DR Dragon Skin+ Nickels. I bent the strings before cutting off the excess and was all ready for a final tune up when I spotted the A string unwinding.

 

All the other string were fine, so I assumed it was a fault with the string. A replacement was sent and, you guessed it, the same thing happened.

 

Any ideas for what I'm doing wrong, given that all the other strings are still fine?

Edited 4 hours ago by Spingere
Typo

[itu]

It seems that the core is round. If you are not careful when cutting it and then with installation, the winding may loosen. 

 

Hexagonal core keeps the winding better in place. 

[Spingere]

I was wondering about that. I've ordered some hex core D'addarios. But still, I must have been lucky with the other four strings.