Loading an image repeatedly in the server throws a 500 Internal Server Error

I had some strange behavior with the server where each time I hit refresh in the browser, some of the images wouldn't load. On the next refresh, these images (that didn't load before) would load and the rest (that loaded before) wouldn't this time. Looking at the console, I saw that the images failed with a 500 Internal Server Error. Requesting an image directly and hitting refresh time after time, it would alternate between successfully showing the image (200) and (304) throwing the following error: "Content-Type header found in 304 response, not allowed" I narrowed this down to Rack's `check_content_type` function in `lib/rack/lint.rb` where it documents this behavior.