Why does nginx remove a / in the URL?

We use nginx as proxy for our play framework 1.2.7 server. Some of the routes in play framework use a <.*> wildcard, the one in question here looks like

GET     /media/{bucket}/{id}/inline/{<.*>config}    MediaCtl.getMediaInlineImgIx

The config can contain a http server and for some reason nginx strips away one of the / in http:// . For example:

13:07:59,299 INFO  [play] ~ Anonymous Guest ~ MediaCtl.getImgIx(): config {"w":100,"h":65,"origin":"http:/localhost:8080","fit":"max"}

when using nginx via localhost:8080. When calling localhost:9010 directly I get

13:19:25,648 INFO  [play] ~ Anonymous Guest ~ MediaCtl.getImgIx(): config {"w":100,"h":65,"origin":"http://localhost:9010","fit":"max"}

I see no messages in access.log or error.log with regards to the URL mangling that seems to occur. Any suggestions on how to fix this?

Answer

nginx merges slashes from URLs on default
see: http://nginx.org/en/docs/http/ngx_http_core_module.html#merge_slashes

You must use: merge_slashes off;