Interactive Rebase: Unable to reorder; unable to resize; says "Blah"

It used to be possible to drag commits in the listbox to reorder them. Now, I find I can no longer drag to lines between commits to insert it–with drag-and-drop, only combining is possible.

Until recently I was able to get around that by simply dragging each commit to the space at the bottom of the listbox, inserting them in the reverse order I wanted--but with the introduction of additional bugs that is no longer possible. The dialog now resizes itself to leave no space, and although there is a draggable bar (mouse cursor changes), it is not draggable–attempting to drag it causes a visual artifact but no resizing.

Finally, on combining two commits, I now see a dialog reading "Blah" (attached).