The “Problem with service” (or “Problem with network”) seems to have been there (for several different network services, not just call forwarding) for a long time. I’ve encountered it in January (so it must have been 4.3 or even 4.2 OS version) when I was trying (as described here) to use the “deflect” function of org.nemomobile.voicecall to programatically forward a call to voice mail.
P.S. Call barring doesn’t seem to have been working correctly, either. Current status is not correctly shown (e.g. I’ve got international outgoing calls barred but it isn’t shown as active) and even if I set it and exit the screen, then it shows again as inactive). It’s been like that ever since I can remember, including the latest 4.4.0.68. XA2 Ultra.