I am sorry for the slow reply - had some technical issues with my gmail. Could you be a little more specific about which interface/workflow you are talking about? I checked the "Group analysis" interface, which launches a pop-up window where the number of genes can be supplied and it worked as anticipated. Just selecting a signature (ie clicking on the signature ID) will not ask for the number of genes.
If you could outline all the steps that lead to this point in the analysis, I will be happy to help you troubleshoot.
Best,
Mario