SDL_PollEvent(&event) not capturing mouse events?

I have a `SDL_PollEvent` loop instrumented like

```
while (SDL_PollEvent(&event)) {
switch (event.type) {
case SDL_WINDOWEVENT:
...
```

When compiled with emscripten this dosen't capture mouse events. I have confirmed, It fires on keyboard and window events. Any ideas on how to further debug?

emcc version
```
evs-mbp:dosbox-staging kevzettler$ emcc --version
emcc (Emscripten gcc/clang-like replacement) 1.39.19 (f45bea21f3a8f74a68ed4e3e3d7e290807ee2aff)
Copyright (C) 2014 the Emscripten authors (see AUTHORS.txt)
This is free and open source software under the MIT license.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
```