Resizing character window differs from vanilla
In vanilla Morrowind resizing the character window does not modify the width of the left column containing Health, Magicka, and Fatigue. This allows the window size to be greatly reduced while still maintaining visibility of the health, magicka, and fatigue bars.
In OpenMW, the left and right columns occupy equal share of the character window, so if the window is small enough the health magicka and fatigue bars become obscured.
See this reference video: