[SalesForce] Perform a SOQL Query LIKE Specifically for Lowercase

Confirming @Eric, your query

List<CustomObj__c> list = [SELECT Name 
                           FROM CustomObj__c 
                           WHERE Expense__Date__c = THIS_MONTH];

is validated by the following:

• Date Format and Date Literals
• SOQL Date Functions

I tried out a version of your query myself, and it worked fine.

Though this is besides the point (the Date Literals work), there is always the option of "rolling your own" by something like the following:

Date startOfMonth = Date.today().toStartOfMonth();
Date startOfNextMonth = startOfMonth.addMonths(1);
List<CustomObj__c> list = [SELECT Name 
                           FROM CustomObj__c 
                           WHERE Expense__Date__c >= :startOfMonth
                           AND Expense_Date__c < :startOfNextMonth];

This sounds like a bug. Please file a case for us.

UPDATE: We're working on a fix.