The nbsp layout's "zwnj2nb3s" variant is only used by the lk layout:
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$ grep -R 'nbsp(zwnj2nb3s)' symbols/
symbols/lk:  include "nbsp(zwnj2nb3s)"
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Unfortunately, when the lk layout was modified from:
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  key <SPCE> { [ space, nobreakspace, 0x100200c, NoSymbol ] };
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to include the nbsp layout the person made errors:
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// ZWNJ on level 2
// ZWJ on level 3
// NBSP on level 4
// Used by lk(sin_phonetic)
partial
xkb_symbols "zwnj2nb3s" {
  key <SPCE> {
    type[Group1]="FOUR_LEVEL",
    symbols[Group1]= [ space, 0x100200c, nobreakspace, NoSymbol ]
  };
};
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