In a text custom field you say you have a single value (say 1650) recorded in one issue and then that same value embedded in a comma delimited list of values:
1) Search for 1650 returns an error. This is because you don't allow a wildcard to be used as the first character.
2) Search for 1650* only returns the issue where 1650 is the only value, excludes the issue that has 1650 in a comma delimited list of other values ... e.g., "123, 1650, 567"
This makes it impossible to find all issues associated with a customer case id number to allow developers to link existing issues or find duplicates, etc.