Commuting - Keen sandals giving me trouble with spd cleats

So I've gotten about 50 miles on a brand new set of keen sandals with brand new SPD cleats and have had to readjust the cleat going on three times already because it seems the cleat is moving. The cleat of course has teeth to grip the sole of the shoe and I've tightened the retaining bolts to what I thing is a reasonable level but I've noticed that my heel keeps finding itself further and further out as the cleat rotates from clipping out. I've backed off the tension on all 4 places on my XC style shimano SPD pedals but as soon as I get home from work today I'm going to yet again have to readjust the cleat. The only thing I can think of so far is that I'm using the phillips retaining bolts that came with the shoe, not allen bolts that usually come with the cleat. Could it be that the allen head isn't allowing me to apply enough torque?

I am guessing you might not get much help as most of your neighbors to the north are still riding in Snow boot:)

I got Keen sandals 6 months ago w/ new SPD cleats and have put over 2000 miles on them with no adjustments. I absolutely love these sandals - cured the hotfoot I was having in other shoes on 30+ mile rides. Friends give me grief for wearing them on rides with temps mid-40s but the rubber toe bumper keeps toes much warmer than you would think ...

The pedals probably are at the loosest tensioning as I was brand new to clipless pedals when they went on the bike. They are Shimano MTB 540's (I think).

LBS put everything together for me.

Cowboy up and tighten the cleats! It's been in the single digits around here, so my sandals are in a deep freeze/sleep right now...

Could it be that the allen head isn't allowing me to apply enough torque?
Probably more likely that the bolt isn't seating properly and loosening up. You might try Loctite if it's getting loose.

Probably more likely that the bolt isn't seating properly and loosening up. You might try Loctite if it's getting loose.

Agreed. I too, have the sandals and find them not the easiest shoes to remove from the cleats. One day, I lost a screw from the cleat and my shoe was stuck in the pedal. I had to remove the entire pedal to loosen the shoe. I made some adjustments and all is good now. As long as I keep the shoes tight around my feet I have no problems getting in and out of the pedals.

Oh, yeah, I did have a little "issue" on my first ride. The sandals were very loose and my foot came out while the sandal stayed clipped in. Just had to make sure the sandals weren't sloppy-floppy on my feet to fix that. No problem with the cleats/pedals though. I did a check and the cleat is still firmly affixed to the sandal.