This is because segmentation filters out all other data as if it doesn't exist. If you have a segment where page = A, that means according to the segment, that's the only page that exists in your report. Since every hit in your segment was page A, you get 100% entry rate.
Use a search filter instead of a segment - it's the little funnel icon in the dimension header. Search filters show/hide data based on your filters instead of completely excluding the data like a segment.
In my example I have page a and filter it out on hit level in a segment. Then I get 100% entry rate.
When looking the entries and visits it is the same amount and when doing a breakdown I see why I have the same amont of visits and entries because it includes all pages which had an entry during my visit on page a. So I still think this makes it too complicatde and not easy for users to work with. The same happens with Exit Rate and Bounce rate as well.
But this is also happening for bounce rates. For example I would like to get a set of pages into s hitsegment how will I get the correct entry rate, exit rate and boucne rate in total? do I have to calculate it or what would be the best solution?
I hope to get a good advice on that!
I think this can get misguiding when trying to get an overview freeform but the values are not correct because it counts all together from the whole visit.
It wouldn't make sense for segments to behave like filters, because filters already fulfill that role in Analytics. If you don't want data excluded via segmentation, I'd recommend simply using a filter.
Can you provide more details on the report you created, and the segment you used?
Entry dimensions are typically visit-based, meaning that they persist on the backend tables throughout the entire visit. This could be a possible explanation, but that completely depends on how you've built your workspace and segment.