Can't upload medium size files via WebUI and commit them.

When I try to include a large file (for instance, file with 5K lines), I can't add it to repo because WebUI hangs on when I click commit button. Fortunately, I can navigate through different panes of WebUI and save the work, but the commit button is in grey state for indefinite time.

Also I couldn't attach to this ticket the large file (>500KB). I believe there are some issues with uploading files. So uploaded the screenshot to 3d party hosting. The issue is reproducible and there is no correlation between different browsers.