دَخَلَ الطَّالِبُ يَبْتَسِمُ.
The student entered smiling.
Here the affirmative imperfect describes the student's condition during entry. Its circumstantial use without wāw al-ḥāl follows the well-known rule. Introducing wāw without considering the structure can shift the hearer toward coordination of events rather than a dependent circumstance.
If an affirmative imperfect does occur after wāw, investigate genuine coordination or another syntactic analysis rather than automatically treating every wāw as circumstantial.