This is probably a known issue. I wonder if anytbody from Apple reads this forum and fixes bugs from user complaints.
I have close to 4,000 messages in my Gmail inbox and more in my corporate Exchange inbox. If I use the search function for text in a message, the search will pull up the message, if it is a recent message which was downloaded to the Ipad. If the search did not yield any results, there is an option to "continue search on server." This feature DOES NOT WORK with either account, as it claims that nothing meets the criteria. I am always able to find the message with web based Gmail, or web Based or outlook corporate email.
Apple - Please fix this.