Durst M600 negative carrier - need help

[AlexanderM]

I'm new to darkroom printing. I printed my first picture using Durst M600 yesterday. The problem is that once 35mm negative strip is inserted into negative carrier and the opening lever is released the negative still not held firmly in position and can be easily moved. This contradicts what the manual says: "When the opening lever is released, the negative will be held firmly in position." My understanding (again from the manual) is that the condenser housing acts as the pressure plate. I'm trying to figure out if I'm doing something wrong or there is a problem with my enlarger.