17.3.4 Synchronization
When the BOD changes mode from Enabled to Sampled mode it needs to re-synchronize to the sampled clock. This is done automatically.
When the sampling rate for the BOD is 1KHz and the BOD is switching from Enabled to Sampled mode, the first sample is delayed up to 1/2 cycle due to synchronization. This only happens on the first sample after changing to Sampled mode.