Created attachment 19433 [details]
repro working copy
attached a simple webapi selfhost solution, after run you can browse
and a response with current time.
but simply adding System.Net.Http reference cause the webapi work only for request while respond not work any more.
in the attachment working copy you can find two commits, the first with the working and the second with the non working.
A working_to_not_working.diff file is provided to show which changes done.