Recently, when I estimate a model similar to Smets and Wouters (2007) using my own codes, the posterior mode I get seems a little strange to me. Specifically, when there is a positive technology shock, the level of output falls below its stochastic trend immediately and persistently increases to a new trend that is higher than the original trend. In other words, output falls given a positive TFP shock. This seems to be inconsistent with the standard results in the literature. But it is not always like this. When I change to another vector of parameter values which is not necessarily the mode, I get the standard impulse responses. This is obviously related to the parameter values. And I think imposing some kind of sign restrictions during the estimation would rule out those unreasonable parameters. And this is just what people do in the sign restriction literature of SVAR. But I am not sure if imposing these sign restrictions has been routinely done in the DSGE estimation, especially behind Dynare.