This happened after a re-installation of the system. All Qt4 applications switched to "plastique" as their default style, and a font looked like Roboto, which, these applications were no longer respecting style settings in Plasma 5. I would like to know if this is a bug, or is there something wrong with my settings.

P.S. I don't want to use qtconfig, as it doesn't change the default style where Qt4 is supposed to detect from my desktop environment.