Normally the default position is for the initial posterior value for a parameter to be taken from the prior, unless the model defines a different method for choosing this.
However in the case of an image prior, the voxelwise value is not used for the initial posterior - instead the existing default prior is used, as if there was no image prior.
It would seem better for the voxelwise value to be used both for the prior and the initial posterior.
This occurs with some models and is generally harmless. However the underlying CEPHES maths library does not allow the messages to be suppressed.
We have bundled a modified version of this library with fabber_models_dsc since it was a significant problem there, however it would be better to bundle this into the core where all models can benefit from it.