Seem that GPxSAT's black flag overlay image only replacing standard icon which originally displayed at the top-left corner of the screen. Due the way of GP4 Tweaker controlling this icon, that "flicker" behaviour will appear if Drive-thru penalty is applied thru GP4 Tweaker's setting, as the same result when we using standard icon.
In drive-thru mode, when penalties has been made then GP4 Tweaker will show blinking black-flag icon to alert player, which also indicating first warning. Because of this, "flicker" is not a correct word, and there's no bug on GPxSAT black-flag image related to this issue.
Also for clearance, GPxSAT project is not mine and I'm not involved with any GPxPatch and/or GPxSAT projects.
In reality, doesn't matter who's
right but most important is who's
left.