Background at corner is not transparent with different OpenGl version.

[Tabi]

I am using a customized widget that is inheriting QWidget and I applied stylesheet to its top level which is as:

@
QWidget
{
border: 10px solid qlineargradient(spread:reflect, x1:0, y1:0, x2:1, y2:0, stop:0 rgba(117, 170, 255, 255), stop:1 rgba(94, 139, 206, 255));
border-radius: 15px;
}@

The corners here are appearing with radius 15px and remaining corner area is transparent I can say remain background out of that radius is transparent. But it is only on my system. If I build and run the program on other systems the background is not transparent in that they are appearing white and it is odd. What I noticed that my system is having OpenGl 3.3 and all other systems are having 4.2 and my question is that is it due to different version of OpenGl? or any other reason? Any help is appreciable, I have no clue why this is happening.

Here are some system related info that are same for all systems:
Qt: 4.8.3 (64bit)
OS: Windows 7
IDE: VIsual Studio 2008
Compiler:MSVC 15.0.30729.1
Processor:Intel(R) Core(TM) i5-2310 CPU @ 2.90GHz, 2901 Mhz, 4 Core(s), 4 Logical Processor(s)