Nope this may not exactly be entirely a bug per se, there was a patch recently implemented in the last Hard Fork 13 to address this same error message but there was also a change made to the ability to upvote with brand new accounts. This problem was especially addressed because it helped sort out an issue when it came to massive bot account creation and abuse as well as an error preventing users from removing their own up votes. I only mention this because I actually recognize the code change from a reply I received on Github about the patch.
The original intent of the recent changes were to encourage user participation and acceptance into the Steemit community before they were allowed to upvote on posts.
You are quite correct in your assumption that (abs_rshares) are a calculated as a result of your current SP which in turn effects your voting power. I'm not sure if this is quite working as intended though, so I'm going to help up vote this post and tag a few people to see if we can figure out exactly how to deal with this. In the mean time, posting and gaining SP through original posts and commenting on existing threads is definitely the way to go right now.
Doing so will both increase your exposure and help gain you upvotes which in turn will translate into more SP and result in a higher (abs_rshares) value.
Could someone else look into this as well, 
I just wanted someone else to double check and weigh in on this to see if it is in fact working as intended or if it needs a bit of a revision because it looks like it may not be working exactly as intended but I wasn't the one to review or push the patch so I may also be incorrect.
RE: (empty)