I am assuming you are talking about the Ladder Memory values (3086 in the dialog, 3107 in the status bar).
The dialog shows the ACTUAL value (reported by the PLC). The one on the Status Bar is "calculated" by Designer. This may be "off" due trailing NOPs in each code-block, rung comment handle values, et. al. It "synchronizes" when you download (it has a "slop delta" that it uses to help "calculate" that number on the status bar, and so this "delta" value is "calibrated" at download time).
Designer determines the precise length at download time. It's an "estimate" up until that point. Even then, the reported value on the status bar may be a little off

.