ID 428077 - Undo gets disabled after using exportImagesFlattened()

Problem summary
Undo gets disabled after using exportImagesFlattened()

Customer reported version
mari.4.6v3

Customer reported platform

Steps to reproduce

1) Open Mari and the example head project 

2) Open the python palette and evaluate the following script:

import marichannel = mari.geo.current().currentChannel()channel.exportImagesFlattened('/tmp/$CHANNEL.$UDIM.tif')

3)  Open the History palette and paint something on the object 

result: notice the History palette does not collect any information after the channel has been exported 

Expected behaviour
It should collect undo steps regardless of the exporting of channels via python 

Actual behaviour
It stops collecting undo steps 

Workaround
Exporting via the UI overcomes the issue

To re-enable use the following: 

while mari.history.isMacroActive():      mari.history.stopMacro()

Reproduced by Manual QA

This bug has been reproduced in:
4.6v3 - CentOS 7 

Unable to reproduce bug in:
4.6v2 - CentOS 7 - regression

Earliest version tested
4.6v2 - This issue doesn't appear in this version and has regressed