Vodafone Germany throttles upload speed

I have a home server in Germany. When I travel outside of Europe and try to download files from my home server, Vodafone throttles the speed to 30-150 KB/s. Files that usually take a few minutes to download take hours.

If I use a VPN or an SSH tunnel based in Germany, there is no throttling. Files download at the normal speed.

I have reproduced this issue from a dozen locations in Singapore, Malaysia and Morocco. When my friends downloaded the same files at the same time from a computer in Germany, there was no throttling.