It has been silent around sh404sef for a while and now suddenly two issues within a few days..
First external 404 components should not be used with the datafeeds component (<skip>reasons</skip>). sh404sef allows to be disables for selected components and that worked fine as far as I know.
It appears that the sh404sef does not correctly redirect POST requests. Is your datafeeds menu ( the one with the issue) your home page ( default page ) ??
With the other issue I noticed that sh404sef replaces the menu id from the correct one ( for example 144) with the default menu id ( for example 109 ) thus pointing to non-datafeeds menu without any valid setting using the default values ( thus english )
I don't have a recent version of sh404sef so I can't investigate whether or not it is a bug in sh404sef. Since the mod_datamenu works fine with normal joomla I assume it is a sh404sef issue.
I have some ideas how to solve/patch the problem, but I can't investigate
When i select a option from the mod datafeed dropdown box i do get the right results. But then when i click on sort to lowest/higest price the mod datafeed shows the initial products from that menu (Men) instead of the lowest/higest results Men/Sweaters.
If i use mod datafeed link in the menu then it sort okay.
Its the same with sh404sef activated (without mod datafeed) or with a deactivated sh404sef = only use the joomla sef