Margin not released after selling BTST (T+1)?

I’m only talking about CNC (delivery/demat shares) here.

When we sell a share, it used to be a pain that only 80% of sell amount is available to use on same day. Last year this was fixed and now a share can be completely switched same day without bank transfers.

But what about Buy Today Sell Tomorrow? I bought Shriram Fin yesterday for delivery and wanted to switch it for Muthoot Fin today. Sold Shriram thinking I would be able to do so, but it did not increase my available margin. Not even 80% was availble.

Can funds from shares sold on T+1 already be used some way, or is this not allowed by design?

As per regulations, the credit from selling T1 holdings (Buy Today Sell Tomorrow [BTST] trades) cannot be used on the same day