Custom Fields Missing From Cache

[Richard Bramley]

In the last week I've come across two separate problems caused by the Contact Get API not returning the values of custom fields using the "return => 'custom_x'" style.  I debugged the code and found that the problem was caused by the custom codes not appearing in a list known custom fields which was fetched from the cache.  Clearing the cache solved the problem.

However, both custom fields were not new.  And both fields have been used previously without a problem.

I've seen a few examples in the forums of people being told to clear the cache to solve problems.  Is this a common issue?  Are there any known permanent solutions?