Resolution: Works As Intended
If you do this step-by-step:
1. Get any kind of pickaxe with three efficiency I books.
2. Put the pickaxe in with one efficiency I, and it should enchant
3. Do that again with the second book
4. Now try it again with the last book. It won't enchant for some reason.
(ALTERNATE) Just use a Eff. II + a pickaxe, and then Eff. I, and it won't work either.
If you use the efficency books II, III, IV, or V, it'll enchant..
The weird part is that eff. II pickaxe + II or III will only stack up to III on the pickaxe, even though it should be a IV or V. Using an eff. IV + eff. II pickaxe will literally SET the pickaxe to efficiency IV, not add to become the maximum of V, and eff. V + eff. II pickaxe will set the pickaxe to a V (but this is necessary as it shouldn't go any further)
This may apply to other enchantments as well, I didn't check that yet. This bug works in both creative and survival (also will probably happen in adventure mode), and it's really, really frustrating.
The attachments are showing an efficiency II pickaxe + the effiency I book.