The problem is that on some platforms, text doesn't quite scale linearly as you increase the point size. Techniques like subpixel antialiasing with pixel-snapping produce shapes that are more readable on low-res screens, but it also causes distortion to letter shapes, and with multiple letters, depending on the exact text and its location, it can add up to amounts significant enough to cause overflow.
It's a problem on any platform that wants more readable text on low resolution. The only platform I know of that chose precise text layout over contrast regardless of the resolution is macOS. On Windows, ClearType still behaves as I described above. On Linux, it depends FreeType settings, which you don't know in advance, so you have to assume that it will happen.
