tree vertical scale not correct when shown in tree viewer (but fine when exported)

The height in pixels of a tree when Fit to window is enabled seems to be wrongly calculated, meaning some leaves are rendered below the bottom margin of the window. This is worse for trees with many leaves w.r.t. height of panel.

Viewing the tree of the uniref50.fa alignment after adding another copy of the alignment to it (so the tree is 30 sequences high) shows this problem. The bottommost leaf is only partly shown.