This doesn't seem like a bug to me.
In the IFC Scheme Settings Dialog you defined the "ALMA quantity" IFC Property, and you set its type to "IfcReal". This means it is expecting a number.
So when you type some text as a default value, I think ARCHICAD will convert that text string value into an IfcReal value, which is zero.
This is why you see zero as the default linked value in the Settings Dialog.
Try to assign a real numeric value in the IFC Scheme Settings Dialog and see what it display in the Settings Dialog.
As another note: I can imagine things are being developed so their more strictly adhere to IFC specifications. Or maybe it was just an overlook of a small glitch in previous versions which allowed it to work the way it did previously.
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