Strongbox does not what it says

Dear Support,

I just opened a Large Strongbox that i curroted...
one of the mods was "items are fully linked"
I droped a six-socketed item wich was curropted but not fully linked...
It is sooo rare to drop a six-linked item, because of this, fails like
this are not allowed to happen... I would appreciate it if you could contact me, maybe ingame because
i am not really familiar with post sides etc.
Thank you

Corruption is applied last and can modify items. So it may have unlinked your 6L or it may have given the item 6 sockets after the linking happened.

In fact, "the corruption made it 6 sockets" is overwhelmingly more likely.

Don't corrupt strongboxes whose contents you actually want.