Double scimitar & Imp.crit

Improved critical for 2-bladed sword works incorrectly with double scimitar. It works, but it takes base crit rate of 2-bladed sword for scimitar also, so both weapons have the same 17-20 cr.

Are you saying that a PC who takes the feat "improved Critical: 2-bladed sword" will get the 17-20 threat range for both a 2-bladed sword *and* also with a double scimitar?

The 2-bladed sword should have a base threat range of 19-20, and with the imp. crit feat that goes to 17-20.

The double scimitar should have a base range of 18-20, and with the imp. crit feat that should go to 15-20.

So If I understand you, you are saying that PCs who take "imp. crit: 2-bladed sword" should have a 17-20 threat range with 2-bladed swords, but a 15-20 threat range with double scimitars - however, the threat range ends up 17-20 for both weapons, is that correct?

yes

Another Custom content weapon type+feats glitch:

Epic Weapon Specialization(unarmed) does not function with cestus weapons. Regular weapon specialization does however.

Also, there's an issue with the cestus weapons. Their description says their base critical range is 19-20/x2, but when equipped, they give the same crit rage (20/x3) as bare fists. This seems to be linked to the same issue as the double scims using the two-bladed sword crit range rather than the crit range it's supposed to have. Whatever the nwncx tweak is doing to apply the default base item feats to the custom base item weapons they apply to, is also forcing the base items to use the same stats as the default base item type. When I come across a maul or heavy mace again, I can verify that by checking their stats vs a warhammer's stats.