  We demonstrate theoretically and numerically that the fundamental Raman
soliton of the widely used nonlinear Schroedinger equation (NLSE) with a linear
approximation of the Raman gain ({\em reduced} NLSE) is metastable. It can
propagate for hundreds of dispersion lengths along the optical fibre before
eventually disappearing due to a peculiar instability, leading to a collapse.
The noise eigenfunction analysis agrees well with the results obtained via
direct pulse propagation simulations. This instability is not present when
modelling the Raman effect via a full convolution, and thus the reduced NLSE
often leads to unphysical results, and should be avoided.
