Vim will move the cursor to the beginning of an object after invoking operator upon it. From an interactive editing perspective this may be considered annoying however it is the consistent choice as operators can be destructive. As such restoring the cursor to its prior position after invoking an operator on an object may not make sense.
There are many ways possible to alter this behaviour to your preference with mappings and/or scripting. But with custom operator mappings this can be particularly ugly.