I am not sure if this will work, but try checking the box in the Spline Properties Manager for "Proportional" before you do the rotate. (I don't have SolidWorks running right now, so I don't know the exact words. Won't be the same in French, anyway!) After the rotate commmand you should be able to turn off the Proportional property so that you can manipulate the spline, if you wish.
Don't worry, Dassault doesn't use SolidWorks to design their planes. They use Catia. That code was written by French engineers, not Americans. Of course, that didn't stop Airbus from having major problems because one group of engineers was using V4 of Catia and another was using V5 and the resulting parts didn't fit properly.
This is not a bug. Uncheck the box for "Keep Relations" (not sure what that translates to in French) in the Rotate Entities tool. Once this is unchecked, it rotates just fine:
I see a lot of your inquiries here and you say they are all bugs with the software, but it appears that you may just need some training on this new CAD system that you aren't familiar with. Please don't refer to these as bugs when they are not.
This spline has no relations at all, so why I didn't pay attention with this check box.
Now, it works, but if no relations, this rotation might be possible, in all the cases.
And I ought not to get a translation, relations being there or not.
So, sorry to insist, but there are at least 2 misbehaviours, with this feature.