"Serif Height" in change weight dialog fixes the wrong nodes when thinning

[Artoria2e5]

I am running FontForge 2017-07-31 on Windows 10 (16299).

I used fontforge's change weight dialog to obtain a more hairline/contrast-rich thing from TeX Gyre Schola Bold 2.005 (sfnt 2.00499, texgyreschola-bold.zip). I selected some glyphs and opened the dialog, asking it to shrink the weight by 30 units.

As you can see in the screenshot below:

• The serif height is correctly detected as 54 units
• Due to the serif height setting, the node 54 units above the baseline is not moved.
• Since fontforge is fixing the above nodes instead of the below nodes, the serif on the straight leg of R ends up moving up.

I expect fontforge to find some other nodes to fix when thinning fonts. For serifs at the bottom, that means the nodes near baseline level.

R, Before:

R, After:

Other letters show this problem as well.

More, before and after:

(I don't think it's quite visible from the screenshot; most of those serifs move up by 20-25 units from the baseline).