Update: Block Producer "EOS Cafe" admits that they were the one to exploit this bug.

See their response here

What is vote decay?

In order to incentivize more active participation in voting, a user’s voting power decays slowly as time goes on unless they recast their vote. This means that votes that are cast today have more total voting power than votes that were cast a week ago, with voting power decreasing continuously over time.
By introducing vote decay, EOS gives voters two options: They can update their vote frequently and maintain full voting power, or update less frequently and have their influence decrease. By incentivizing users to update their vote on a regular basis, it gives users the opportunity to reassess block producers regularly and to decide if they should be changing their vote for any reason.

More info here

What bug is being exploited?

In EOS, you must stake coins to get voting power and network resources for your account. However, somebody else can stake their coins to your account as well. To give an oversimplified explanation of this bug, it is possible to refresh somebody else's votes, without their consents or knowledge, by transferring and staking a small amount of EOS to their account. This means that vote decay is basically gone, since anyone can refresh your votes back to maximum voting power.

And Block Producers are doing just that.

Why do I think this is wrong?

Block producers exploiting a bug in the protocol that they are trusted to run on behalf of the community.. is just wrong. This is akin to an elected government official exploiting a loophole in a law that was never intended to be there - absolutely disrespectful to the elected position that they hold.

If you claim that it is not wrong to exploit this because its "just the current design", they you must also agree that smart contract hackers are not wrong in stealing a hundred million dollar because it was also "just the current design". The whole ethos of EOS was to get away from "code is law" and honor the intended design of a system, rather than the implemented design of that system.

This is bad for EOS and BPs who exploited this EOS Cafe has betrayed the community's trust and should be ashamed.

If you still think it's okay because it's just part of the protocol, would you still feel that way if BPs exploited a more serious bug? What if they exploited a bug that transferred all of your coins to them? The severity of the bug is hardly relevant. The point is that BPs are trusted, elected position - and exploiting a bug in the very protocol that they are trusted to run is hugely problematic.

Original source is from reddit here

The user that made the post on reddit is u/UnknownEssence and I will sent him the rewards from this post after communicating with him.

Hope next time he prefers steemit for his post! ;)

PS1: I would appreciate if someone makes an investigation to find out which other BPs exploited this BUG except "EOS CAFE". I know that after 27 April 2019 some are quite easy identifiable since there are some drastic changes in votes because of the bug.I will upvote 100% comments that help to that direction! Thanks!

PS2: I am invested in EOS and I want transparency as more as possible about BPs. It is important to identify BPs with low Ethics. This is a good opportunity to identify some of them. Vote only BPs with proven integrity. Thank God we have much of them waiting down the line ;)