Strange behavoir of fixed spacer when applied to last system of a page

7f9585a, self-built, Windows 10

1. Take My_First_Score
2. add a "Staff spacer fixed down" to measure 6
3. add a page break to measure 8 -> the spacer's bottom end seems to be in mid air (exact same lentgh as before this step, 7sp), rather than now relating to page bottom
4. add a page break to measure 16
5. add a "Staff spacer fixed down" to measure 14 -> the spacer goes from bottom staff line of measure 14 to top staff line of the system above (length goes negative in Inspector, -23sp)
6. add a "Staff spacer fixed down" to measure 30 (some measure in last system) -> it goes from bottom to top of that measure's staff lines (length goes negative in Inspector, -4sp)
7. delete the page breaks -> only the 1st spacer looks OK again, the 2nd now goes up from the bottom of the 3rd system to the top if the 1st, the 3rd spacer still covers only its own staff lines, i.e. none changed its length or direction

My expectation would be that in all these cases the spaces defines the exact distance of the staff to the bottom page border, just like the 'normal' staff spacer down does set the minimum distance to the bottom page border or always behaves like in step 3, i.e. start on bottom line of staff and goes down 7sp by default