Apparently if you call an emergency number from your Android device, you can't block calls for the next 48 hours.

We don't know why this is the case, though we imagine it may be to prevent you from blocking your local police department or other emergency personnel.

The notification appears at the top of the Call Blocking screen. It does not provide a rationale, nor is this all that happens after you call for help. Your phone also blocks data for five minutes, possibly due to internet usage interfering with calls and texts on some networks. We have not tested whether toggling airplane mode serves as a workaround, and I'm not sure testing out a phone feature ranks as a good reason to dial 911.

Left: Call blocking disabled, Right: Data connection disabled

We don't know if blocking call blocking was started by a Dialer update or an OTA. Feel free to hit us up in the comments if you have an idea.

Source: Google+

Thanks: Austin Hill