My new phone (Verizon Droid Maxx) does not always route my international calls through Google Voice, and I do not understand why or how to fix it.

I set the Google Voice settings to make all international phone calls using Google Voice. However, I took a detailed look at my bills for the last couple of months since starting with the Droid Maxx and noticed that some of my international calls were not being routed through Google Voice.

Most international calls were being routed by Google Voice, but a significant minority were not, and it has been costing me quite a lot of money. Has anyone encountered this issue or have any idea about how to fix it?

I did not have this problem on my old Samsung Droid Charge.

Carrier: Verizon Wireless
Device: Motorola Droid Maxx
OS: Android
Encountered: 11/13-2/14 (from when bought Droid Maxx through today)