Why this should be happening only to me I don't know but several searches through the forum had no result so I figure at the moment I'm the only one with this problem.
What I do is this: First I click on the 'Populate' button of the population I want to edit so I can see the instances. Then I go to the 'Editing' tab of that population and click on 'Start Editing'. Now the instances get an orange colored bounding box when i hover with the mouse pointer over them. I click on an instance, the axis arrows appear and I can now move the instance. When I'm done moving the instances I click on 'Stop Editing'. Now I create a GIC file. While this is being rendered the instances disappear from the preview but re-appear when the render is done. But the moved instances did return to the position they had before I started editing. When I do check the box the modified instances are highlighted. The alternative way of editing instances with the button above the 3D preview produces the same non-result. Oh, and while editing the preview render is paused.
TG v3 build 126.96.36.199
Andy, I assume you 'saved' after you stopped editing?
I'm not sure what's going on but I'll have a look.
@ choronr: Yup, I did save after I moved the instances.
@jo: Thank you. If you need the gathered project (214MB) tell me where I can park it so you have access.
Could be TG3 did not install correctly: There are no temporary output files (the folder is there but is empty) at the default location and the Automatic Render Output Files do not show up at all.
Will uninstall/reinstall to check if this does correct the situation.
Edit: Uninstall/reinstall did correct the situation: Instances stay where I put them. ;D
Please let us know if you have problems again. I'm not really sure why reinstalling would fix this.
Regarding the automatic render output files, these would only be saved if you check the "Automatically save all renders" option in the Rendering preferences panel.