Hello db10,
I haven't noticed the behavior you observed, so I attempted to reproduce this result with ADAU1701 and -1452 as shown here:
With these examples I didn't observe the DC residual. However, you may be using a different DSP or a more complex signal flow. I'm not aware of anything in the DC Block filter that would "memorize" a previous audio signal, but perhaps additional processing between your DC Block filter and Level Detector could introduce or amplify that. For example, a compressor in between might provide a very high effective gain at no signal, which could exaggerate any residual DC.
As a solution, you might insert a second DC block immediately before the level meter and/or DAC. If you're using the ADAU145x, make sure to download the latest SigmaStudio release (it fixes a problem when two or more DC Block filters are used in the same project).
Best regards,
Bob