Placing blocks instead of breaking them

When you press the LCTRL button and the destroy button, you will place blocks instead of breaking them. I checked the controls. it's not because LCTRL is the sprint key (I swapped it to the Z key and it still happened). please help
Info:
the bug happened on creative vanilla 1.8.3 and on the april fools snapshot (15w14a)
how to recreate:
1. hold a building block (or liquid) in your hand and select it from your hotbar
2. press LCTRL on your keyboard
3. you will break blocks instead of placing them.