Filename presented in UTF8 fails

I have an generated curl (or wget) command where the file name is presented in (some sort of) UTF-8 format: '--output-document '=?UTF-8?B?cHJldXBncmFkZV8xOV9jYnVpbGRfN19sZi56aXA=?='' .

This will be downloaded as 'preupgrade_19_cbuild_7_lf.zip' , but cliget will actually makes file '=?UTF-8?B?cHJldXBncmFkZV8xOV9jYnVpbGRfN19sZi56aXA=?=' .