RTL8139, RealHW: network is hanging after uploading of text file

When I try to upload text file (lorem.txt for example) using Firefox (v43.0.4, client side, ReactOS) to HTTP File Server (2.3i, server side, Windows 7), network stops working: upload is never finished, pings starts failing.
Downloading of text file have no problem, uploading of binary files - works fine too.
When ReactOS started in debug mode, uploading works slow, but not causing any hang (but I am anyway attaching debug log: debug_net_fine.log).
Installation of official Realtek driver (Realtek RTL8139/810x Family NDIS 5.1 Drv, 5.505.1004.2002) fixes the problem.
Tried to test this scenario using QEMU (which have emulated RTL8139) - it is not reproducing there.