not necessarily deliberate, but people don't understand that glassworkers don't always have complete control of the material with which they work. "the glass has a mind of it's own many times", and it is not afraid to speak it.
I've many times had red go orange after reheating.
Most collectors have no idea of the difficulty of batching colors and actually getting them to work with each other. It's been said many times that the Germans had a saying and that was that a formula couldn't cross the street. meaning that just because one company could get the results they wanted from a formula, didn't mean that it could be replicated by others. Size of furnaces, source of raw materials, heat sources, etc. all have major effects on the final result. That's why so many studio artists and many smaller companies use the premixed color rods from Kugler, Reichenbach, Gaffer, and others for their color and then encase them in crystal. That's been going on for many, many years.
It's the same as with making good wine, cheese, cooking, etc. The one in control and the ingredients they use and their equipment can make a lot of difference in the final outcome. Even freshness has a bearing in mixing glasses. If an ingredient is allowed to sit too long and absorb any moisture, that can throw off the calculations of mixing the ingredients by weight which is normally the case. the difference between a 3% moisture content and 20% is critical. Have you ever tried to measure the moisture content in chemicals? very difficult.