I've been having this strange issue with saving parts as STL files since using SolidWorks 2018, and I finally remembered to make screen captures so that I can ask about it here.
This issue crops up roughly 40% of the time when I save a part as an STL file and it is driving me mad, because the only way I have found to 'fix' it is to close down SW and open my part again, so I hope someone here may be able to shed some light on why this is happening and what I can do to fix it.
What happens is this: I regularly export files as STLs for 3D printing purposes, and because SW has the y-axis as up instead of the z-axis up like most 3d-printers have, I have learned to insert a custom coordinate system that has z-up that I can use as the output coordinate system when saving as STL.
This used to work flawlessly in SW2017. In SW2018 however, seemingly randomly, SW decides to change the orientation of my parts as if this custom coordinate system was the default coordinate system before saving the STL. This causes the bodies in my part to visually change orientation and outputs an STL in which the parts are still oriented the wrong way. So it negates my fix for correct orientation for 3d-printing and forces me to open the STL in another program and rotate the parts to the right orientation manually, which ads unnecessary extra work. I have noticed that the first export with the desired output coordinate system selected after building or opening a SW part file always works as expected, and the issue only happens on subsequent STL exports from the same file.
About half the time this issue happens, after I save the STL with the parts mover around, the parts even keep being displayed as having changed their orientation in the SW main window. Because everything is displayed in the wrong position though, this prevents me from being able to work on the part any further. If I then mouse over the construction steps in the feature tree, I do get to see the orange edges preview of the parts in their correct orientation. So it appears that SW does 'know' the correct orientation still, but displays the parts as if the second coordinate system is now the default. (I don't have screenshots of this right now.) This is sometimes fixable by going into one or more features and okaying out of them again, or changing some value for a feature and then okaying out. But often the only way to get my correct display back I need to exit SW completely.
Does anyone know what could be happening here and what I can do to prevent this in the future? As I said I haven't found any clear reason for this happening and it appears to happen quite randomly but far more often than is good for my sanity. (Maybe a bit more with more complex parts, but as you can see from the screen shots above, pretty simple parts also get messed up like this.)