yes....according the design of SCT and MCT, the possibility of mirror slopping /shifting are higher. Mirror moving inside...only one side focusing method. So, the mirror will not be moving in very accurate. I think everyone using SCT or MCT will experience this.
But it also caused by the weight of the mirror and angle of the OTA pointing to.
what do I mean by weight of the mirror? Means that if the diameter of the mirror is more than 8"...the weight of the mirrir will be unacceptable.
why ETX facing minor mirror shifting? I personally tested it before. Besides of shifting, slopping also available.
How to eliminate this situation? Maybe we can add a focuser or do some trick s on the focusing shaft to temporary remove the shifting but not slopping.
If you are planning to do astrophotography, this will be your main enemy.
Now, how angle/position of the scope will bring the slopping along? As we know, mirror moving in SCT or MCT only be controlled by a focucing shaft. So, plus the focusing shaft cannot really hold the weight of the mirror, then the mechanism between the mirror and draw tube(is this the right words?) is not really fit enough, slopping problem will occur.
So, now I assume that you all know what the heck is shifting and slopping problem, and these are my personal opinion.
Actually I already fix this two problem recently. But I also spent quite a lot on something. At the end, I am not doin this becoz of astrophotography. I like to see DSOs in wide field.
Universe24, the points that you mentioned are correct. Sharpness and dark background that ETX gave us are excellent. Actually we are the winner in light polluted area. But once we get into the dark site,definately we will be the losser to those using big guns. But something that we can change so that we will not be always a losser.

I won the heart and impression from lot of observers last saturday night with my mighty wide field ETX125. I can't imagine that I can get a wide field of M42 & M43 area by using my 26mm. Try to imagine how about if I put 32mm,40mm or RINI 52mm ep. Impressed! Interesting! I also done a sketching on wide field M42. I like astro-sketching nowadays. I think I will put down my camera and film then hold a pencil and eraser in every single abservation.
Hope all of you feel not sleepy and boring when looking at this message.
good luck to all of you.
Tommy