It's been like this since I started seriously base editing over a year ago. It aggravated me to no end that my emblems would change on their own in the same way you've described. What I found, for example, was that if I already had some of the short glass items and I placed another with a different emblem, after I exited the base that newly placed one would change to match the ones already there. Sadly the only way to repair that was to yank all of those short glass items and place them all again with the same emblem. You simply can't have more than one emblem on the same item, even when in different rooms. It's aggravating, I know, but at this point there's not much to be done for it.
<head on desk>
Thank you.
Though, your avatar cheered me up.
Problem: Unable to permanently change SG emblems in base on glass and floorplates.
Before:
If I moved or sold and repurchased just one item ( one of the two glass pieces, for example), it would change all the other items of that type throughout the base.
Now:
The same method temporarily changes the emblem. It will do so while in the editor and for a time. When exiting the base and returning, I find that the SG emblems revert to whatever they were last.
Did things change? Do I now have to sell every single item of that type to change emblems or am I just doing something wrong?