A TAC engineer finally explained what changed from CCM 4.1(3) to 5.1.
Here is his reply
Progress Indicators are used for informational feedback. In this case this parameter determines whether the alerting progress indicator to Inband Information is reported to digital PRI gateways.
The setting change did not affect any other offices because Telco is not sending us the:
RX <- STATUS message with the * Cause i = 0x82E31E - Information element not implemente*.
Now with this setting change, since Disable Alerting Progress Indicator = False, we ignore the message and do not release with a * Cause i = 0x82E5 - Message not compatible with call state*.
Before in CM 4 by default CM ignored the *Information element not implemented*. Now in CM 5 we need to disable the Progress Indicator so CCM does not send *Progress Ind i = 0x8088 - In-band info or appropriate now available*, this way the Telco will never send the *Information element not implemented*, and we will not disconnect.
So the change is in the way CCM acts when facing the *Information element not implemented* message and the call is not connected yet.