font problem after updating sdk from 3.x to 4.x

Hello.
After upgrading to version 4.0.2 I have a problem with fonts.

As you can see from the image, the background of the text is no longer transparent.

I use the following code to have the second hand always-on:

function onLayout(dc) {
if(Gfx has :BufferedBitmap) {
offscreenBuffer = new Gfx.BufferedBitmap({
:width=>dc.getWidth(),
:height=>dc.getHeight(),
:palette=> [Gfx.COLOR_DK_GRAY, Gfx.COLOR_LT_GRAY, Gfx.COLOR_BLACK, Gfx.COLOR_WHITE, Gfx.COLOR_BLUE]
});
} else {offscreenBuffer = null;}
curClip = null;
}

if I delete the highlighted string I have no problem.
unfortunately I need the string to limit the use of memory.

does anyone know how i can fix it?
thank you.