Default ZW cell data usage not right

My plan starts on the 22nd each month, and I use this setting to track network data: #NTMTHM22#

Its been working properly for a long time but recently seems to show only the current days usage. I've tried other pre-built network codes in the widget and they all show the same value, except for "last week" which shows a different value. This seems to have started in the last couple of weeks although I can't think of a change that might have done this.

Any ideas?
Nexus 4, Cyanogenmod 4.4.4