ProcessUpdate of the dimension triggers processing of all partitions of all measure groups in the cube

I have Account and Customer dimensions in the cube that are connected to the same measure groups (there are about 15 - 20 measure groups in the cube). When I run XMLA command to process update these two dimensions, like this: My Database Dim Customer ProcessUpdate UseExisting in the case of Account dimension it finishes in a couple of minutes because it doesn't trigger processing of all partitions of all measure groups. ***But*** in the case of Customer dimension it triggers processing of all partitions of all measure groups, so process update of this dimension lasts longer then full processing of entire cube. I am not sure what can be the reason from which the dimension will trigger all this processing in the case of one dimension and not in the case of the other. For both dimensions Process affected objects is set to Do not process. Where should I look, what to check, can I somehow prevent this reprocessing happen? Thanks!