can' t reproduce this on ubuntu 15.10

For me this still happens , may be it is only for particular graphic card ( mine is nvidia gtx 750ti) I am on arch linux.
here is the video (dropbox-link)

notice the icon changes to ' - ' but the canvas keeps on zooming.

let me know if you want any logs or details

Edit: now that I see it more closely, I think it only does what is checked in the tool option, regardless of the icon change when Ctrl is pressed. this might be confusing. And i request making ctrl press zoom out behavior available

I have the same problem. I use Krita 3 on Linux Mint.

Pressing 'Ctrl' makes the icon change to '-', but it still zooms in.

Also another behavior when I trigger the click with my tablet :

• I keep pressing Ctrl : the icon '-' appears
• With the tip of the pen I touch the tablet : the icon '-' changes to '+' again.
• I release the pen : the zoom in is triggered.

Furthermore, in the tool option, pressing Ctrl doesn't change the case checked.

Edit : With Ctrl + Alt the zoom out works, but in the tool option, the "Zoom in" stays checked.

hm... maybe a conflict with cinnamon then?

Maybe.

This afternoon I was checking the file /libs/ui/flake/tools/KoZoomTool.cpp, some part of the code seems suspicious for me. I tried to understand how the code works, and for me the Zoom Out is never triggered.

KoZoomTool does look like a dusty old bit of code... hard coding ctrl key support in D1115 seems to do the trick for me.