Custom Fields Not Updating

I created identical custom fields for my Leads, Contacts, and Opportunities.

Upon conversion of my lead, all of my lead data is properly copied to its corresponding custom Opportunity and Contact fields, just as it should be. Great!

Now the Problem - If I change any custom field data in the Opportunity or Contact records, it DOES NOT UPDATE to the corresponding forms.

IS it supposed to, or am I pushing this CRM beyond its design limits.

Any feedback would be greatly appreciated!

DSG