Hello,

This lighthouse model: http://www.thingiverse.com/thing:19786

I sliced it (a few different times, different settings) and printed it several times, each time there was a slip on the Y at around 5-8mm off the bed, same direction.

I haven't had this happen for ages so I spent a while hunting an issue, the problem still occurred, I scaled the model by 10% and it worked fine.

I guess it's just one of those bugs, but might point to something in the slicing operation, can anyone concur?

Slicer 0.9.2
0.25 infill
0.3 nozzle, 1.75

It's probably not an issue with the slic3r, it's more likely an issue with the printers Y axis, the GCode that happens to be generated likely exposes an underlying issue.
Does the preview in Repetier host or similar GCode viewer show the "Slip"? if not it's the printer.

I'd try the usual things
Turn the axis pot up slightly
Turn the axis pot down slightly
Check for interference in the Y axis

I think its a stepstick issue, swapped it and its working. I tried playing with the pot however there was no sweet spot.

Any idea why a slip problem due might occur at the (exact) same point in a print every time? print shape was pretty similar on each layer

Try lower speed or acceleration and see if the slip happens at the same spot. Also check for grooves if you are using linear bearings. Also check the jerk settings.

And it would help if you said "between window and door" or something to let us visualize where your problem is.