Currently, the Block of Copper is treated like any other variant of copper that can be chiseled to. This is a problem, since a Block of Copper can be turned to 4 Cut Copper in a Stonecutter. The Cut Copper can then be chiseled back to a Copper Block, repeating the process. meaning you can duplicate Copper Blocks infinitely with only a Chisel & a Stonecutter.

While it's not as convenient, Blocks of Copper should not be compatible with the Chisel.

that's only for 1.17. For 1.18 onwards, it gives 4 blocks of cut copper
This isn't a bug. Since this is achieved through intentional behavior, it's an exploit, hence why I haven't tagged it as a bug.

This exploit works for all versions 1.18+ on all versions that support Cut Copper. I am using the latest version of Rechiseled.

Here's a screenshot from the history section of the Minecraft Wiki

As far as I can tell, the copper block to cut copper ratio is just 1 to 1. (On Minecraft 1.17 that is at least)

Also, please use the correct template, bug in this case, as that requests the info I need.
What version of Minecraft are you playing on?
What version of Rechiseled are you using?

Wouldn't Block of Copper be better to exclude from the Chisel than Cut Copper? Since Cut Copper is meant to be decorational & 4x easier to get in bulk than the base block.

Meh it could go either way.
I feel like some people might try to chisel the copper block and not realize they need the cut copper, this way it is the same as for other materials.

Might change it depending on what Mojang does with the new copper blocks in 1.21.

Should be fixed now for all the 1.18+ versions. Thank you for reporting the issue!