I think this raises from the fact that they are the same id but different damage values.
RP2pr2 Marble is 122:0 and Basalt Cobble is 122:3 so I guess it just doesn't pay attention to the damage values.
 
															
		[Bug 1.15, 1.23] Miner placing RP2pr2 basalt cobble turns it into marble
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			Nice catch. It was mentioned in the additional pipes thread as well, was that you? Anyway good thing to not ignore metadata  
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			- Official Post
 Fixed for the next release, not worth a hotfix though. 
 
		