preamp inverts polarity

Well, relative to Kaitty at least I work in the live sound business, where in his case he seems to work only for the cheap shot. 

I have a tube preamp that inverts polarity (for some reason it is designed that way).  I reversed the speaker connection on one of the speakers, and it sounded better to me.

Playing a test record confirmed my suspicion.

The catch is:  not all of my records sound better with the speaker wires reversed on one speaker.  I would say 80% of my records sound fine either way (I can't hear a difference), but some (those with good sound staging) have improved "imaging" (if I am using that term correctly).  And a few "image" better the other way.

This makes no sense to me.  Is "phase inversion" the same as "polarity inversion"?  And why do some recordings seem to have it backwards?

And why would anyone want to change both speakers? 

preamp manufacturers say both speakers, if you only do one then the speakers are out of phase.  that is one woofer goes out while the other goes in thus canceling the bass out.

The speaker cables are marked differently so you can get both speakers wired consistently.  They are not made of different materials designated only for + or - . 

Are the tires on your car for only going forward?   Reverse the wires and be done with it.