Issue with Start and End of Selection numbers changing

Hi all,

I am new to Audacity so apologies in advance if this is a silly query or a very simple fix.

I am using Audacity to anonymise (with brownian noise) parts of wav. files and I am manually putting the numbers into the Start and End of Selection boxes. My issue is that often (not every time but about a quarter or a third of the time) when I go to put the end of selection numbers in, the start numbers randomly change. As I said it doesn’t happen every time, but enough to make it annoying and time consuming to keep going back to check every time. Does anyone know why this is happening or what I can do to stop it?

Many thanks in advance!!