hi.
1. try a quick check by displaying durations (such as total float) either:

a) usingsubunits of the duration units (e.g. 11d 2h)
or
b) using1 or even 2 decimal points for duration units (e.g. 11.25 d)

you can do this under Edit / User preferences / Duration format

for a number of reasons your total float (or any duration value) may not be an integer in the time unit you selected as your display unit (e.g day). especially if you use dateand time (hour of the day) for start / finish dates (manually input, calculated depending on duration type or imported from external applications).

this way -11.25d or -11d 2h would be displayed as -11d (unless you change your preferences as described above), but still would not be returned by the filters "less than (or equal to) - 11d" as you would expect.

2. clicking "go to" in the relationships tab always displays the predecessor / successor activity , adding it to the current layout regardless of any current filter(s). this is because P6 assumes you wanted to view its details. reapplying the filter (or reloading the layout containing the filter) will hide it again (if it is not returned by that filter or combination of filters in the first place).

hope this helpes

Tibi