There are a couple of things going on here, let me try to clarify:
1) Jonathan is correct, the top entry box is for running searches. If you type "Psalm 49", you are telling Accordance to find every location of Psalm 49 in the title portion of commentary, whether referenced explicitly or as part of a range. This may or may not take you to the section on it, but this is what you are asking Accordance to do.
2) If you search instead for =Psalm 49, you are asking Accordance to find every instance of just Psalm 49, so a hit for "Psalms 1-50" would not find it. This is generally more accurate at jumping to that place in the tool.
3) Flex vs Exact doesn't really matter much here, it applies more to word variations and word combinations, not the range of verses.
4) The best way to jump to the specific passage in the tool is as Jonathan said, to put the passage in the GoTo section. For almost all of my tools this works flawlessly, jumping right to the top of the section.
5) I say "most" because as you accurately point out, rari, WBC is a bit inconsistent in actually jumping to the top. I'm actually not sure why it does this, but I have a feeling it could be some tagging errors in the tool - Rick or someone else who helped with the tagging may be able to clarify. WBC is an extremely complex tool, so this may just be something funny going on with that, that can be cleared up.