JavaScript is a case-sensitive language, which is generally a fine feature, but it makes typing in legal JavaScript a little harder than it might be. The problem is when you created a property and don't remember exactly how you used camelCase in it. For example:

MongoDB shell version: 2.1.0-pre-
> user=

{firstName:"Jim",lastName:"Smith",ZipCode:12345} { "firstName" : "Jim", "lastName" : "Smith", "ZipCode" : 12345 }

> user.zip // hit tab – command completion doesn't work because you spelled ZipCode with an initial cap
> user.ZipCode = 98765 // if command completion was case-insensitive, it could correct your typing in its completion
98765
>

The code that provides the command completion is in JavaScript and is doing a simple string comparison of possibilities with what we are trying to match. See shell/utils.js and matching code in shell/mongo_vstudio.cpp .

if (p.substr(0, lastPrefix.length) != lastPrefix) continue; // skip items that don't match (my comment)

It could easily do a case-insensitive comparison instead.

if (p.substr(0, lastPrefix.length).toLowerCase() != lastPrefixLowercase) continue; // set up lastPrefixLowercase before loop

The code would always return the case-correct completion, so this is just a convenience in typing, making the tab completion feature a tiny bit more useful. The cases where users would be annoyed by seeing case-insensitive matches seem likely to be fewer than the cases where this would be helpful.