Spite PP reduction gone after battle

[YuzzzzuY]

Fought a battle against a wild Ghastly, who used Spite. This reduced the move of one of my pokemon to 0. When the battle was over and I encountered another pokemon, the move that was supposedly reduced to 0, had recovered to same pp prior to Spite. I must say that I'm not entirely sure whether the pp reduction caused by Spite is supposed to be permanent or not, I couldn't really remember and looking it up didn't really tell me much.

Steps to reproduce/breakdown of what happened:

1. Encountered wild Ghastly with Pichu

2. Ghastly uses random move

3. Pichu uses Charge Beam succesfully, PP drops from 5 to 4

4. Ghastly uses Spite, PP of Charge Beam drops from 4 to 0

5. Pichu tries using Charge Beam, but fails since no PP

6. Pichu wins the battle regardless and encounters new wild Pokemon

7. PP of Charge Beam back at 4.

Note: I'm not sure whether step 5 is needed to reproduce it, but thought I might as well mention all that happened for complete picture. Also I didn't check the PP after the battle with Ghastly, so I'm not sure whether it was already back to 4 then and whether starting a new battle was needed to reproduce.