Can we take rulings from a reliable scholar but who has one questionable practice?

Can we take rulings from a scholar who is usually aligned with the sunnah and has proven his knowledge by consistantly providing reference from Holy Quran and hadith correctly but has the habit of making dua after fard prayers and saying ameen loudly(Almost all imam in my country do this)? Does this make him Ahlul bidah and are all his fatwas regarding other matters become invalid and unacceptable?