ID 326694 - Progress dialog moves down every time it is displayed (Linux)

Problem summary
The progress dialog moves down the screen every time it is displayed.
This is only an issue in Linux.

Customer reported version
nuke.11.1v1

Customer reported platform
centos7

Steps to reproduce
1) Open Nuke

2) Create a CurveTool node (Right click on the node graph > Image > CurveTool).

3) In the CurveTool properties panel click 'Go'.

4) Click 'Ok' on the 'Execute' window that appears.

5) Wait for the progress bar to complete.

6) Repeat steps 3 to 4 and notice that the progress bar moves down.

This issue can also be reproduced with other nodes that use the same progress dialog, such as the Write node.

Expected behaviour
The progress bar should be displayed in the centre of the screen or where it was last shown.

Actual behaviour
The progress bar moves down the screen every time it is displayed. 
The image below shows the progress dialog moving down every time it is displayed (left to right).

Workaround
Unknown. 

Reproduced by support
This bug has been reproduced in:
Nuke11.1v1 - CentOS 7
Nuke11.0v3 - CentOS 7
Nuke11.0v2 - CentOS 7

Unable to reproduce bug in:
Nuke11.1v1 - Windows 10 - MacOS High Sierra
Nuke11.0v1 - CentOS 7 - Windows 10 - MacOS High Sierra
Nuke10.5v7 - CentOS 7

Earliest version tested
Nuke10.5v7 - This issue no longer appears in this version and has regressed