Issues with Scrolling Index to End

I am using RH 2022.5.28 to generate frameless output.  I recently noticed that if I try to scroll to the end of the index, I can only see part of what I think is the last index term, and the scroll box (thumb) almost completely disappears. See image below showing, on the left, the scroll box near the bottom of the Index and, on the right, the scroll box almost completely hidden, with what I think may be the last index term only partially visible.

Is anyone else seeing this?  It only occurs on the Index tab. It does not occur on the Contents tab. If it matters, the frameless layout I am using is based on the default Orange template.