Strange error with font 6 and 7 when fgcolor != bgcolour

[obdevel]

I have a strange issue when using font 6 or 7 and the foreground and background colours are different. It causes the hardware interrupt to be suppressed (INT0), i.e. my ISR does not run. It's fine with font 2, or with font 6 and 7 when the fg and bg colours are the same.

This suggests line 918 in TFT_ILI9341.cpp, and the subsequent code path.

I can workaround by blanking the text before redrawing, but this causes flicker and slowdown at fast update rates.

I'm using an ATmega1284P chip with the MightyCore Arduino core.

Thanks.