I started the migration from Qt 5.6 to 5.10.1 and faced with this problem. On 5.6 ver the style was "windowsvista" and all works well. Now it looks like Qt can't detect this one and use "windows" style.
Moreover, on my PC, the build of 5.10.1 looks good. It works on Windows 10 x64, same as buildbot.
Configuration line:
-release -prefix C:\repository\x64\qt5 -force-debug-info -platform win32-msvc2013 -nomake examples -no-compile-examples -nomake tests -opengl dynamic -opensource -confirm-license -mp -no-strip
I build Qt without Ruby and Perl libs, because it's unnecessary for my project.
Maybe the problem in configuration, because in 5.6 there was configureapp.exe in /qtbase and now I can't see it. But I do not understand the reason.
I found a problem. After Qt5.10.1 the "windowsvista" style becomes a plugin. So in the final deploy file windowsvistastyle.dll schould exists. I add a folder "/styles" with this .dll and a problem is gone.