Scoreboard objectives with "_"/underscore doesn't work anymore with @e

Scoreboard objectives with an underscore in it e.g. "is_bonus" doesnt work properly when used in a commandblock or chat.
Im not sure if this is really intended, because before the w26(/w25) update, everything with this worked fine.
So to test this i made an entity, type WitherSkull and gave it a score from "is_bonus"=1
To kill (only) this entity (or do other things) i did this via commandblock

/kill @e[type=WitherSkull,score_is_bonus_min=1,r=3]

But since w25/w26 this doesn't work anymore. It doesn't even throw an error oder message in the chat. It only works, when i am removing the score checking.

/kill @e[type=WitherSkull,r=3]

Im a bit confused, because this seems only to affect testing entities. @p seems to work

There was a Ticket back int 1.6.2 which was "solved" (MC-25174).
But then im not sure why this worked in the snapshots (and 1.7) after this fix...