My mouse button 4 in combination with a modifier key is being inputted as mouse button 5

My mouse button 4 does not function properly when using a modifier key at the same time such as shift or sprint. My friend plays on 1.8.9 also and has no problems using both mouse button 4 and 5 while using a modifier key. I saw a report was already made for this bug, but it was labeled as resolved and my problem is not resolved.