Zhu Xi's Legacy Crossbow Tech (Fire second bolt) Incorrect behavior or description

Me and my friend went to test Zhu Xi crossbow technology that is supposed to fire a second bolt on crossbows.

Initially we thought it would fire a second bolt to deal same amount of damage as the first one.

We went to test and watched replay on slow motion:
Normal bolt fired damage 19 (+11 vs heavy)
Secondary bolt fired damage 8 (+4 vs heavy)

Even the description on unit UI displays these damages.

I don’t know which of the following is the correct statement:
-Is it a bug that it is dealing less damage.
-It is not properly informed on the technology description.