Ok Now seriously, I checked the Poser versions and compared when using the option to reload the textures and overwriting a texture. I did not change any cache settings! All worked as it should on my side no issues in any poser versions. some slight glitches yes but always ended up loading the new version. P13 latest release once did not want to load so I just jumped out of the material room and back and all was just fine. But have to say this method is not secure for creations, you lose time checking if everything worked right, you can't jump back undo redo, so really uncommon for texture creations or applying them! 

I do allot of texturing and always when working real time save the altered texture under a name that fallows 01 02 03 04, I can roll back compare the final will have the appropriate name. your workflow is clean and secure, and for sure not a time loss.

All Poser versions seem to be acting the same using the reload. A update suggestion for the "Update texture feature " would be to add visibel button in the material room for the ones who like to overwrite the texture maps.