No more transparency for font background on bufferd bitmap since SDK 4.0

Hi, 

I use a bufferedBitmap with color palette and custom bitmap fonts without antialiasing.

Since SDK 4.0 the font background  is not more transparent. The color is defined before:

dc.setColor(CustomColor, gfx.COLOR_TRANSPARENT);

The code is running many years without problem.

I don't understand, what's going wrong with new SDK