Over time I would expect the membrane to suffer local damage and allow bulbs to come through; but certainly not in less than a year! Were you at home when the mebrane was laid?

I saw it down before the pebbles were put down. Should I complain?

It rather depends on what they charged and which grade of membrane they used - the cheapest, 'weed suppressing' type membrane sold at garden centres is very thin, and it wouldn't be impossible for a bulb's topgrowth, with its pointy tip, to penetrate through the membrane if it was really thin, but it's not all that common for this to happen.

They should have used a more heavy duty geotextile, so if the one you saw laid on the ground wasn't shiny looking with a green line here and there (the next available, slightly more heavy duty and slightly dearer one at the garden centre, usually), but instead was like a dull, black fabric, they've used cheap liner. Whether they charged appropriately for using that, I don't know.

The other option is, they laid the liner in strips without sufficient overlap and without pegging down the joins, and as they spread the stones on top, the fabric beneath has moved. Might be worth rootling around where a bulb has appeared, trying to grab the edge of membrane, if its there, to see if that's what's happened. If that's the cause, then you should complain.

I would complane as the obvious whole idea was to stop plants from underneath . the biggest cost would be labour and the stones . the membrane would be minimal in comparison .