Performance regression in cygwin 3.4.0

[tryandbuy]

Reading from stdin is very slow when a process runs outside of Cygwin Terminal.

Steps to reproduce:
1. Create "test.txt" file using python code:
long_text = "10" * 2500
with open(r'test.txt', 'w') as f:
    for i in range(5000):
        f.write('KEY%03d: %d => %s\n' % (i % 100, i, long_text))

2. Install "cygwin" package version > "3.3.6-1"
3. Open windows command prompt (cmd.exe)
4. Enter command:
type test.txt | c:\cygwin64\bin\wc.exe -l

When running the same command (use cat instead of type) on the Cygwin Terminal, no performance issues observed.

The last version of cygwin package without issues: 3.3.6-1
Versions of cygwin package with issues: 3.4.x - 3.5.x

P.S. I tested this combinations of pipings:
cygwin_prog | win_prog    # no issues
win_prog | cygwin_prog    # has issues when running in windows command prompt, no issues in Cygwin Terminal
cygwin_prog | cygwin_prog # has issues  when running in windows command prompt, no issues in Cygwin Terminal