This behavior is ON by default. If you do not want the cursor change on a meter or button, set MouseActionCursor=0 on the Meter or button.
Example of disabling mouse cursor change:
[Meter]
Meter=Image
W=100
H=100
SolidColor=0,0,0,255
LeftMouseUpAction=!Execute ["http://rainmeter.net"]
MouseActionCursor=0
Note: If you have a button with a meter (either image or text) on TOP of it, you will need to set MouseActionCursor=0 on the image/text meter even if it doesn't have a mouse action, or the button will not change cursors.
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