File-Transfer with Range-Header is cached on iOS

I am using the Range-Header to download only a portion of a file from a server. I've seen in the server logs, that after some requests the app just pulls bytes from one of the previous requests out of the cache (I suppose) and gives them back. That leaves me with 3-4 parts that are OK (downloaded correctly) and i.e. 30 duplicates which are supposed to be the rest, but actually got "downloaded" from the cache. My temporary solution is a to append a arbitrary GET parameter to the url, that changes on every request (i.e. timestamp) and that is not processed. But that is only a quick hack, since this cannot be intended, I think.
EDIT: Maybe I should add that I could only observe this behaviour on iOS. Android or requests with a normal HTTP Client work fine!