Cannot convert Blueprint Function Library inputs to local variables

When a blueprint function library function has input variables, the input pin cannot be converted to a variable / local variable.

Regression:
No - same behavior occurs in 4.16.3

1. Open UE4 Editor (any project)
2. Add blueprint function library asset
3. Add input variable to New Function 0
4. Right click variable pin

Result:
Options to "Promote to Variable" and "Promote to Local Variable" are grayed out for the input pin

Expected:
Blueprint function library functions can convert input variable to local variables