ID 435284 - nuke.message() and nuke.alert() don't wait/pause the main thread

Problem summary
nuke.message() and nuke.alert() don't wait/pause the main thread

Customer reported version
nuke.12.1v2

Customer reported platform
centos7

Steps to reproduce

1) Open Nuke

2) In the Script Editor run the following code:

nuke.message('Test 1')

nuke.alert('Test 2')

print "foo"

Expected behaviour
For foo to be printed after both dialogs have been closed.

Actual behaviour
foon was printed, showing that the main thread isn't halting/waiting

Workaround

from PySide2 import QtWidgets

QtWidgets.QMessageBox(QtWidgets.QMessageBox.Information, "Nuke", "Test Message", QtWidgets.QMessageBox.Ok).exec_()

print "foo"

Reproduced by support
This bug has been reproduced in:

Nuke 12.1v2 - Windows 10, CentOS 7.7, macOS 10.13

Nuke 12.0v1 - Windows 10, CentOS 7.7, macOS 10.13 - regression

Unable to reproduce bug in:
Nuke 11.3v6 - Windows 10, CentOS 7.7, macOS 10.13

Earliest version tested
Nuke 11.3v6 - This issue doesn't appear in this version and has regressed