I believe this is working as intended, as all flowers that have a guaranteed drop when broken (without silk touch or shears) can not be replaced when trying to place a block in the same position, and wildflowers always drop when broken.
This appears to only happen if the TNT isn't sitting on a block when ignited. Ex. Having a block of TNT on a block in the air, igniting it, and breaking the block shows expected behavior, but having a floating block of TNT and igniting it shows the jittery behavior.
Jeffery Cooper
I believe this is working as intended, as all flowers that have a guaranteed drop when broken (without silk touch or shears) can not be replaced when trying to place a block in the same position, and wildflowers always drop when broken.