Metoject Pen

I have been giving myself a methotrexate injection once a week for the last few years. Anyone else who has the same medication, will probably have been switched (like myself) to the new self injecting pen type injection (Metroject). Apparently this is the way to go and the other injection form has been discontinued. I got my first batch of 4 last week, and when I took off the yellow cap at the end, the needle shield seemed to be stuck to the device. no matter how hard I pushed the cap to start the auto injection nothing happened. I tried another one, and it worked first time. With this one when I took off the yellow piece at bottom of injection, I heard a click, and about a half inch of needle shield was showing, which moved when I pressed it on skin, then another click when I pushed the start cap, and the injection was administered without me feeling a thing. Has anyone else who have been moved to these pens lately, had any problems with them? I took the faulty one back to the chemist, as the needle shield is fused to the syringe. Hopefully it's just a one off faulty one, although I am going on holiday next week with the 2 left from the same batch.