When I visited viabtc, I always saw it's already in 0 free submission. If it's a visual bug then I don't know the reason behind it but I haven't heard or notice about viabtc having a visual bug on their website.
The visual bug was probably about the 19 free transaction acceleration slots that were displayed for almost an hour and yet when one tried to enter their TX I did, an error "Submissions are beyond limit. Please try later."
Did you read
hosseinimr93's explanation above? It's not a visual bug; they have a limitation as explained by hosseinimr93. They don't want to fill the whole block with a very low fee while they can get far better fee from the block mined.
Or maybe viaBTC is pushing for their paid and premium services right now?
LOL. I guess it's unlikely that they are trying to manipulate this. Looking at the paid accelerator fees, I doubt anyone thinking of paying a low fee, would be using such a paid service & they know that as well.