Enter the following:
A1: 1
A2: 2
A3: =A1+A2

Mark A2:A3 and select Edit/Copy.
The clipboard now contains the formula, but one of the dependencies is missing.
The application/x-gnumeric target is rendered as:

<gnm:ClipboardRange>
  ..
  <gnm:Cells>
    <gnm:Cell Col=\"0\" Row=\"2\" ExprID=\"1\">=A1+A2</gnm:Cell>
    <gnm:Cell Col=\"0\" Row=\"1\" ValueType=\"40\">2</gnm:Cell>
  </gnm:Cells>
</gnm:ClipboardRange>

In this situation, OpenCalc replaces formulas with unselected dependencies with constants. This is a sensible solution. The example above would become

A2: 2
A3: 3

The more complex 
source:

A1: 1
A2: 2
A3: =A1+A2
A4: 4
A5: =A3+A4

with A2:A5 copied to clipboard, would give

A2: 2
A3: 3           <-- converted to constant
A4: 4
A5: =A3+A4      <-- still a formula