Imprecise slews after successful model building

At our recent trip to Lake San Antonio and afterwards I had a strange problem:

I polar align my RH200 scope. I build a model - RMS < 5.0.

But the slews are very imprecise.

SGPro can still center the object.

Afterwards, tracking is very precise.

...

I spent a lot of time trying to figure out what's happening. Some observations:

• the slews are always the same, i.e. a star always ends up in the exact same place on my image (somewhere in the lower right corner)
• building the model with more or less points has no impact
• tried various parameters in the 10Micron handset (with / without refraction correction, set refraction parameters by hand, switch from J2000 to JNow in the ASCOM driver...) - always the same

I posted in the 10Micron forum, but nobody had a good idea.

Then, in the last nights I first thought that I figured something out. After model building I could slew with the handset to a start and it would be precisely in the center! But then I realized that TSX had still subframes on. When I turned them off, the slew were as before.

...

THAT was the clue! Normally, the slews should be precise with or without subframe as the subframe should be in the center of the image!!!

More analysis. Yes, ModelCreator creates a subframe in the lower right corner of the image (it uses width/2 for width AND left side and height/2 for height AND upper side!!!)

Once I used no subframes, everything worked again. Yei! Martin (he creator of ModelCreator) told me that he'll fix this in the next release of ModelCreator.

... but it cost me several hours of imaging time at Lake San Antonio when the Meridian Flip failed due to this issue ... :-(