Thanks for using salmon! This is certainly not expected behavior, and I can't see anything obviously wrong looking at your command line parameters and output. Could you provide a bit of detail about how the alignments were generated (e.g. what aligner, version number, and options, and the reference to which you aligned)? Also, out of curiosity, could you tell me what output you get and if the behavior is any different if you don't modify the default --incompatPrior? Finally, would you mind moving the issue to the GitHub repository instead? That will make it easier to track the issue you're encountering and any code that may need to be modified to address it.
Thanks!
Rob