From your images, it doesn't really look like there is a problem. In order for your app to run it does need to use memory. Depending on what you do it will use different amounts.
Using [NSString stringWithFormat:@"%d", myCount];
requires more than you might think because you are asking the system to parse your format string and inject parameters into it. Parsing and scanning a string isn't a trivial operation.
In a number of cases when memory is allocated for a task it isn't released. This is usually the case when it's expensive to create (like the scanning structure, or parts of it) or is likely to be used repeatedly.
You should be worried if the memory grows bigger each time you do the same activity and return to your 'transient' state. Consider running multiple iterations of your button push and, between each push, take a heap shot. If each heap shot (apart from the first and last) are empty (or very close to it) then everything's good. If not, it will show exactly what isn't being released.