Derived patterns introduce additional radicals while the hollow weak radical remains subject to iʿlāl.
PatternHollow wāw exampleHollow yāʾ example
Ifʿālأَقَامَأَطَارَ
Istifʿālاِسْتَعَانَاِسْتَعَارَ
Iftiʿālاِجْتَابَاِخْتَارَ
Infiʿālاِنْقَادَاِنْقَاضَ
اِسْتَعَانَ — يَسْتَعِينُ — اِسْتَعِنْ
Translation: He sought help — he seeks help — seek help!
Forms such as مُخْتَارٌ can, in different contexts, express agent or patient meaning. Do not determine voice from isolated spelling alone.