As previously discussed in IRC, but now I seem to have found a semi-reliable reproducer:

• Open simplebrowser
• In place of the default tab, open https://sapo.pt (also seems to reproduce when leaving the default tab open, but this possibly makes it more reliable?)
• Open a new tab with https://www.ipma.pt/pt/otempo/prev.localidade.hora/index.jsp#Lisboa&Amadora
• Click the "Selecione a Cidade/Vila" dropdown and close it again

When the dropdown closes, one of three things happens for me:

• The rendering flips upside-down:

• The tabbar and UI vanishes, with the rendering turning brown instead of blue, and the font looking slightly off:

• The rendering turns black completely

Which of the three happens seems to possibly be connected to the window size (so if you can't reproduce, try restarting simplebrowser and resizing the window before the next attempt).

After the initial failure, resizing the window seems to fix things, and I haven't been able to reproduce the bug again without restarting simplebrowser.

Clicking still works (but with the original, unflipped coordinates), and if the rendering turns black, the drop-down still renders fine when clicked.