I haven't seen this, but I've seen some goofy iMessage behavior lately in iOS8 for various friends.
I would try signing in and out of iMessage, just to give it a little settings "kick in the pants" and see if it helps.
Settings -> Messages -> Send & Receive. Then click on your Apple ID and select sign out. Then click where that was to sign back in.
After you sign out and sign in, be sure to make sure your phone number is selected in "you can be reached at" and as the "start new conversations from."
If that doesn't help, keep an eye on your network connectivity when this happens. Curious if you on/off wifi and on/off cell data.
