Variable tweens are not setting the variable to starting value at creation.

[VanCastar]

When creating a variable tween, the starting value is not set as the variable value when creating the tween. The variable is refreshed only after the next pass.

And this example quits instantly.

The only way to work around is to set the Variable as 255 before the Tween starts OR start the tween AFTER the variable checking

Windows 10 with GDev version 5.0.140