We have seen some unusual behaviour of a trigger from a button causing the Qaction to run twice. We have checked all other params and trigger points but it is only this Write Button that calls the Qaction. We have tried to remove the pop up message to see if this was causing the problem but it doesn't appear to be. Has anyone come across this before? 
Hi Rebecca,
Is this button parameter supposed to set another parameter? If not, the setter="true" attribute should not be present on this parameter. It not being able to set a different parameter is probably resulting in it setting itself a second time, triggering the QAction again.
Let us know if this doesn't resolve your problem, and we'll try to recreate the problem first.
That worked, thank you!
Great thank you Floris, we will try this and report back