First of all the alignment of each character gets disordered and text becomes hard to read after using converted texture packs
To re-produce this bug, you have to
1. Open Minecraft.
2. Select a converted texture pack (for example 32x32) with custom bitmap font.
3. Close Minecraft.
4. Open Minecraft.
5. Hardly readable text!
The converted texture pack should be available for you inside the attachments.