Rendering artifacts starts to show up on the text after resizing and/or changing font (OpenGL)

Tried running "/examples/widgets/charactermap -graphicssystem opengl". Initially it looks fine. But switching between different fonts and font sizes for a bit and some artifacts on the characters show up (usually on the bottom of the glyphs/letters). Maybe the textures for the bitmap fonts are not cleared entirely/correctly (maybe bad dirty regions)? Not sure.

I've also seen similar issues when running the following applications. In some of them you have to play around with the font and font size before it occurs:

/demos/textedit
/demos/books
/demos/spreadsheet

Attached a screenshot that shows stray pixels on several of the glyphs.