[phenixbb] on HIS ** both conformations clash in the flipping

Dear All, In the log output of the Phenix refine, for the flipping of the N/Q/H residues before XYZ refinement, it often occurs something like "HIS ** both conformations clash, **PLEASE CHECK MANUALLY**". Will you please tell me what will clash with 1 of the 2 conformations of the specified HIS? I have checked the specified HIS in Coot, and I still do not know what does it mean for "both conformations clash". I am looking forward to getting a reply from you for clarification. Smith