That's hard to tell without knowing how your data model and data looks like and what exactely you are doing when entering another tab.
I assume you are using an action to make a selection which isn't anymore possible after applying the section access data reduction, hence the selection is actually cleared.
If possible, create & upload a small sample QVW that demonstrates your issue, if you need further help.
I'll try to work on getting a sample QVW that replicates the issue but in essence yes it seems that QlikView realizes there isn't any data there and clears the selection. Unfortunately, we need it to not clear the selection so I'm trying to see if there may be any workarounds to this.
Thank you for the quick response!
It's not quite clear for me but it sounds that you hadn't enabled the option "strikt exclusion". Without these option is section access only a kind of usability and not really restricting data to the user-rights. Take a look here: Section Access: Strict Exclusion and here for more helpful informations and examples: Section Access.