I’m being thick, right?

Ok, I’m sure I must be doing something stupid, but I can’t figure out what…

I’m simply trying to remove a SRAM force chainset from a bike I bought recently. I know the non-drive-side crank should self-extract with an 8mm Allen key.  However,  when I try that, instead of the bolt pushing against the cap that sits over it and removing the crank, instead the whole assembly – bolt and cap – unscrews.

I’ve tried tightening the cap as much as possible, and greasing the head of the bolt. Nothing’s worked yet.

I’m currently waiting for a decent dose of Loctite to set before trying again, but do any of the experts out there have any bright ideas if that doesn’t work either?