I haven't had a chance yet to test whether this is a behavior with just the Baseball relic or whether it is a faulty interaction between mods. However, during a Construct run with Replay the Spire and Hubris loaded, I had created a copy of Defense Mode that was duct-taped to Reinforce. Defense mode costs 0 by default and Baseball had reduced the cost of Reinforce from 1 to 0. When the cards were combined, the resulting card cost 0. However, later in the run, the cost of the card had become 1, the cost you would expect if the cards were duct taped together without Baseball. I am not sure when exactly when the change occurred, but it may have been when I upgraded the card, or possibly when I saved the run and resumed later.
I haven't had a chance yet to test whether this is a behavior with just the Baseball relic or whether it is a faulty interaction between mods. However, during a Construct run with Replay the Spire and Hubris loaded, I had created a copy of Defense Mode that was duct-taped to Reinforce. Defense mode costs 0 by default and Baseball had reduced the cost of Reinforce from 1 to 0. When the cards were combined, the resulting card cost 0. However, later in the run, the cost of the card had become 1, the cost you would expect if the cards were duct taped together without Baseball. I am not sure when exactly when the change occurred, but it may have been when I upgraded the card, or possibly when I saved the run and resumed later.