If you fire a dispenser, that has more than one glowstone, into a respawn anchor and power it once it will use 2 glowstone and only restores one charge...

Steps to reproduce:

1. Place a dispenser pointing into a respawn anchor
2. Put more than one piece of glowstone in the dispenser
3. Power the dispenser, observe the amount of glowstone used...

Expected result: one piece of glowstone is used and one charge is returned
Outcome: two glowstone is used and one charge is restored

Additional notes:
Happens using any power source - Lever, stone button, wood button

Reproduced on Windows 10 and Android