Question to Subscriptions

[Azurel]

In my "Subscriptions" I see all domains with two different icons:

/theme//icons/16/plesk/subscription-status-ok.png
/theme//icons/16/plesk/subscription-status-locked.png

"/theme//icons"

My question is:

Two domains are locked with hint:

The subscription is locked for synchronization: It is excluded from syncing with the service plan because the subscription parameters were customized.

I don't understand. Why this two domains are locked? What can I do to unlock it?

 

[Azurel]

Any hint for this?