Hotbar keeps changing to 8th slot whenever the keyboard appears

I'm trying enchanting my sword using command but the slow keeps changing to 8th slot and the sword not enchanting.

 

Steps to reproduce:

1. Put sword in all hotbar slots except 8th slot
2. Open chat box and the keyboard appears
3. Type /enchant @s sharpness 5 and click enter
4. The hotbar switched to 8th slot and can't be enchanting