I have discovered that some files can't be changed when using different subpacks (if experimental features turned on), while without experimental features, it works fine.

Here are the blocks / items I found that can't be changed (so far):

• All torches
• All rails

There is a resource pack in the attachments here for download - look at the subpacks inside the pack, and check it twice in-game (with experimental features, then without).

Hope it was clear and for any further questions, I'm ready to answer.