Twisting/Weeping Vines not 100% drop with shears

Weeping and twisting vines do not have a 100% drop rate when using shears, which they should do as per the wiki and Java edition.

Steps to  reproduce:

1. Set random tick speed to 0 to stop vines from growing.

2. Get a stack of each vine and some shears in your inventory

3. Set gamemode to survival

4. Plant a stack of either weeping or twisting vines

5. Harvest vines with the shears

Expected result: You collect 64 of either vine

Actual Result: You collect approx. 20 of either vine.