You may be using the same colors, but the palette index has been reduced, see first image. If I load up the common safe palette that is packaged with OXCE's installer LibreSprite already reindexes the palette to the correct values to preserve the colors (see second image).
You can find mentioned palette under ".\common\Palettes\UFO-JASC-SAFE" of OXCE installation folder.
Edit:
Looks like you managed to fix it while I was posting. Good on you.