Question: Strange Errors?

I find I have a number of strange and unrelated errors.  I am new to Maple, but have been using Mathcad so am somewhat familiar with these systems. 

One of the problems I have has to do with confusion between literal and standard subscripts.  I find it difficult to get Maple to recognize literal subscripts using any of the recommended methods.  When I do get it to work, and I'm not sure what I'm doing wrong, when I paste pieces of code into another document the literal subscripts don't behave as literal subscripts anymore.  A similar problem occurs when I use the greek letter delta with a latin letter as one variable name.

Another problem I encounter is with naming variables.  Occasionally I'll delete any references and expressions containing a particular variable from a document.  When I recalculate the worksheet, the variable continues to hold a value.  The Variables pallett will not unassign the variable when I try, although the option is allowed.  I have to close the document and reopen it to get the desired result; no variable or no value or both. 

Help! I want to do work!