I have had a look at this and I cannot find a way to block the message that is causing the problem without causing other problems elsewhere.
The best that I can do at the moment is to provide an option [isolate] on %ww that will fix the problem locally. For the next release the following code will work correctly with this option.
winapp
Program Test_Radio_Button
integer :: iw,winio@,ipos,jpos,lw_handle,irb
irb = 0
iw = winio@ ('%lw&',lw_handle)
iw = winio@ ('%`ca[Test]&')
iw = winio@ ('%rb[RB1]%nl&',irb)
iw = winio@ ('%gp',ipos,jpos)
iw = winio@ ('%ww[no_sysmenu,isolate]&')
iw = winio@ ('%`ca[Window]&')
iw = winio@ ('%sp&',ipos+20,jpos+20)
iw = winio@ ('%4bt[Close]')
end