Question:

If the purpose of a COLA is to maintain the buying power of a previously determined value, under what theory does the VA decrease my caretaker's benefit based on my Social Security Retirement COLA?

Jim's Reply:

Hmm...that's an interesting definition of why there is a COLA .
 

However, since it's well known to those around me that I'm no financial wizard I'll just say many social welfare benefits are offset by other social welfare benefits to prevent what is often called concurrent receipt or double dipping. 
 

When social welfare benefits are awarded for a similar cause there are often dollar limits that restrict the overall dollar amount that the beneficiary receives. This is very common with all sorts of state and federal benefit awards. If you receive a benefit for a low income situation and that situation changes, the benefit will adjust accordingly.
 

Is this palatable for everyone? No, I guess it isn't. Is it legal? Sure it is...you just have to read the fine print for the benefits you receive.
 

I can't address your situation directly since I don't know the authority that provides your benefits but in the end, offsets are routine to prevent concurrent receipt of benefits.