When an application is run with minification alternatingly enabled and disabled, it can happen that the browser uses a cached minified asset when minification is actually disabled.
The problem is that both the minified and un-minified versions of an asset are served from the same URL with the same Last-Modified header.
The cleanest solution would probably be to serve minified assets from a different URL, like we do for gzipped assets.
If we don't want to do that, we could also check the Etag in addition to the If-Modified-Since header in the asset request. Currently, if the If-Modified-Since date is after the lastModified date, a 304 is sent regardless of whether the Etags match. However that would mean that the browser could never cache both the minified and the unminified versions of the asset.