In the meantime there is a viable workaround.
Open the files Data\PlayerProfiles\Default\inputconfig.xml and Data\PlayerProfiles\Eoc\inputconfig.xml from the game directory.
Search for the texts "MOUSEBUTTON1" and "MOUSEBUTTON2" and replace all instances to "MOUSEBUTTON2" / "MOUSEBUTTON1".

There should be 2 lines you'll have to change in each file.
Default\inputconfig.xml:
Code
<!--  default mouse bindings -->

<IE_MouseButtonLeft 	pikey="MOUSEBUTTON1" ...
<IE_MouseButtonRight	pikey="MOUSEBUTTON2" ...


Eoc\inputconfig.xml:
Code
<IE_Action1 		pikey="MOUSEBUTTON1" ...
<IE_Action2		pikey="MOUSEBUTTON2" ...