Replicable!! WordPress redirect loop on contribution page with short code

I don't know the fix to this but after spending more time than I should admit to trying to diagnose it I have finally figured out how to replicate it!

1) Clean Civibuild of wpmaster
2) Download & install https://github.com/eileenmcnaughton/nz.co.fuzion.eg
3) change the contribution page #1 to not use a confirmation page
4) go through the front end to the contribution-page shortcode url, fill it in & submit. It will go into an endless loop "The page isn't redirecting properly"

What's going on? I don't fully know but the only thing in the eg. extension is this

function eg_civicrm_post($op, $objectName, $objectId, &$objectRef)

{ civicrm_api('Setting', 'get', array('version' => 3)); }

The issue is not affected by using civicrm_api vs civicrm_api3 and that IS a valid api call that should return without error.

The endless redirect is happening with it being passed in the skipToThankYouPage function
to the thankyou page.

CRM_Utils_System::redirect(CRM_Utils_System::url('civicrm/contribute/transact', "_qf_ThankYou_display=1&qfKey=$qfKey", TRUE, NULL, FALSE));

However, the required information is not stored in the session / cache when it gets to the page.