Doesn't really feel like a bug to me, it's just that the replace filter doesn't auto link anything that you're linked to with C, nor does it keep the link in if you replace a linked block with the same block type since it's basically removing the original one (which includes the connections) and replaces it with whatever you have selected.
It's unwanted behavior though, improvements:
- if you have a C connection, putting down a block through replacing should auto link it if possible
- if you don't have one and the block to be replaced is linked, and you replace it by the same block, the link should not be removed