Automatic inadvertent changes when file is opened

[kopeckyf]

Opening Libertinus Serif Italic in FontForge and saving it immediately (CTRL+S) without touching any glyph results in some automatic changes. There are about a dozen of them, here is one example: (Anything between [-...-] is removed and replaced by {+...+})

StartChar: longs
Encoding: 383 383 499
Width: 299
GlyphClass: 2
Flags: MW
LayerCount: 2
Fore
SplineSet
463 698 m [-1028,20,21-]{+1028+}
277.152249135 429 m [-2,22,-1-]{+2+}
 231 195 l [-2,23,24-]{+2+}
 197.2 26.8 168 -121 121 -184.2 c [-0,25,26-]{+0+}
 97.5 -215.8 59.2 -233 7 -233 c [-0,27,28-]{+0+}
 -27 -233 -66 -212 -66 -187 c [-0,29,30-]{+0+}
 -66 -165 -48 -150 -33 -150 c [-0,31,32-]{+0+}
 -15 -150 1.1 -161.9 12 -182 c [-0,33,34-]{+0+}
 18 -193 22 -197 38 -197 c [-0,35,36-]{+0+}
 57.9 -197 70.8 -190.4 84.5 -160 c [-0,37,38-]{+0+}
 120.2 -80.7 114 -15 168.6 276 c [-2,39,-1-]{+2+}
 186.5 372 l [-2,40,41-]{+2+}
 189.4 387.3 184 391.4 166 392.6 c [-2,42,-1-]{+2+}
 130 395 l [-1,43,44-]{+1+}
 124 410 123 417 134 425 c [-1,45,46-]{+1+}
 165.881330125 428.446630284 192.565483863 429.665899259 204.456347867 449.769256815 c [-1,47,48-]{+1+}
 223.766589369 534.695776328 254.148305186 606.786528856 304.400390625 651.299804688 c [-0,49,50-]{+0+}
 338.5 681.5 381.799804688 699 437 699 c [-0,51,52-]{+0+}
 511 699 585 634 585 588 c [-0,53,54-]{+0+}
 585 554 559 533 537 533 c [-0,55,56-]{+0+}
 512 533 495 551 495 579 c [-0,57,58-]{+0+}
 495 619 495 624 477 648 c [-0,59,60-]{+0+}
 467 661 443 666 427 666 c [-0,61,62-]{+0+}
 407 666 364 662 330 602 c [-0,63,64-]{+0+}
 297.96628699 545.324969289 289 491 277.152249135 429 c [-2,22,-1-]{+2+}
EndSplineSet
Refer: 421 305 N 1 0 0 1 279 0 2
EndChar

The font compiles just fine with or without these automatic changes. I'm wondering how I can disable such changes, as they make it harder to contribute to the upstream font repository. Or maybe these automatic changes are in fact desirable and should be changed in the upstream font?

I'm using FontForge 20190801 on Fedora 31.

[skef]

The removed content doesn't seem to be in the current version of the file linked to or the version that was current when this was filed. That makes it harder to track down any discrepancy.

In any case the removed values are TrueType "point numbers". Given that these glyphs consist of Cubic Bezier contours I'm not sure why they would have TrueType point numbers -- I don't believe FontForge normally offers that combination as an option. On the other hand Libertinus has long been developed in FontForge so I'm not aware of why they would be removed now and not before.

No further information at this time but I may check into this in the future.