also i remember previous to Dec 2016 when you went out at Mae Sai and went to Tachiliek immigration you were photographed and registered on computer and your details were printed out on a official looking document which was then stamped and you paid 500 baht, on returning document you got your passport back already stamped out, nowadays none of that only a green slip to recieve passport back, so my thinking is thats why the only do day passes nowadays
Marcus if you are going to Mae Sai,,you can park your bike,,if you arrive at Mae Sai just carry on to your left going down to the river and turn right at the bottom and just on your left hand side is a backpackers hotel with parking then 5 mins walk back to border control if this helps
as i posted a while back last time i was at Mae/Sai Tachiliek doing a border bounce,,young couple was refused entry at the land crossing even though they had a Myamar visa and Tachiliek said no must fly in this border only for day pass,,,,,and those were there words
no if you go Mae Sai / Tachiliek they issue 1 day border pass if you tell them you are shopping which they will ask and must return to Thailand same day