The semi-vowel substitution does not take place in the case of aṅga (stems) ending in bhū or the word sudhī before affixes beginning with a vowel.,
Thus प्रतिभु - प्रतिभुवौ, प्रतिभुवः; सुधी - सुधियौ, सुधियः ॥ 6.4.77.,
न भूसुधियोः
Adhyāya 6 · Pāda 4 · Rule 85