Modal Dialog requires 2 clicks of ok to close, Modeless only 1

[qtnewbie2017]

Linux Touchscreen Device.
[1] Creating simple MessageBox (0k button) using exec() requires 2 clicks to close
[2] Creating one with msgBox->setWindowModality(Qt::NonModal); msgBox->Show() requires just 1 click.
If do not call msgBox->setWindowModality(Qt::NonModal); in [2] then need 2 clicks.
So seems if window is modal need 2 clicks.
Any ideas what could cause this? The message box itself is being created as result of push button click