Cura confused as to what's touching the buildplate? I'm very new to 3D printing, but so far I've been able to print a couple things off Thingiverse without issue. However, as I'm trying to print another part, I've run into a situation where Cura is totally confused as to what's touching the buildplate and what isn't:



All I did was use the "mirror" feature to put it in a better orientation for printing....

Any ideas what's going on here? I'm using Cura 3.4 for Linux.



Update: I tried using the rotation tool instead as suggested by Oscar, but I get the same result:



Update 2: Hmm so even when I just import the part without doing anything else, Cura is still confused:
The up- or down-ness of a part is its Z-orientation, which is specified in STL. It looks like whoever published that STL file published it upside down, requiring you to flip the part or rotate it by 180. You can flip it in Cura as you've done or leave a comment to the author of the STL that the part is upside down.  However, the author may not know how to fix this because low-end modeling tools typically do not have the capability of flipping a model. In these cases, using another tool such as Cura or Slicer can generate a right-side up model. Cura seems to like generating AMF files, so I use Slicer to generate STL files for upside down models. Once you correct the STL file, you'll be able to import the model directly into Cura right-side up.