Dimmer switch peculiarity

[DKL]

I've just bought 2 Green-i motion detector light switches for the landing - small children up in the night, can't do switches etc. The first I fitted instead of one (of 2) 2 way switch and it works fine. This powers 2 bulbs at full brightness, comes on as you approach, goes off at given time etc

The second I fitted again instead of one 2 way switch and at first I though it was faulty as it flashes (there is a light on the switch when the lights are off) and the light bulbs did too. This switch only powers 1 bulb. Looked for a poor connection, found none. But if the bulb is only run at a very low output then it works fine. If I use the dimmer facility to make the bulb brighter then it gets a bit brighter but them starts flashing and goes off. It gives the impression of being overloaded but doesn't trip the trip switch and the switch is rated to 300 watts and its only a 70 watt bulb.
The original 2 way on/off switch works everything fine.

I tried this second dimmer switch in place of another single way switch and it works fine. I suppose this test doesn't check the strapper/common connection so I shall try the second dimmer in place of the first in due course.

All dimmable halogen inside light bulb type bulbs.

So could there be a reason for this in the house circuit or should I still suspect the switch?

[Alucidnation]

Some dimmers have a minimum loading as well as a max.