Linq interaction

Linq objects refer to an internal object, they are not cloned

Currency oldCurrency = new Currency();
oldCurrency = (from c in lrc.Currencies where c.CurrencyID == id select c).Single();
System.Data.Linq.Binary tms = oldCurrency.Tms;
mCurrency = (from l in lrc.csTtaCurrency_U1(mCurrency.CurrencyID, mCurrency.Name, mCurrency.ShortName, oldCurrency.Tms) select l).Single();

This code leaves both oldCurrency and mCurrency with the old value.
To have them refer to the new value, lrc.Refresh is needed. In this case they will both refer to the new currency. To have oldCurrency refer to the old, and mCurrency to the new, you have to make a clone:

Currency oldCurrency = new Currency();
oldCurrency = (from c in lrc.Currencies where c.CurrencyID == id select c).Single();
oldCurrency = (Currency) oldCurrency.MemberwiseClone();
System.Data.Linq.Binary tms = oldCurrency.Tms;
mCurrency = (from l in lrc.csTtaCurrency_U1(mCurrency.CurrencyID, mCurrency.Name, mCurrency.ShortName, oldCurrency.Tms) select l).Single();
lrc.Refresh(System.Data.Linq.RefreshMode.OverwriteCurrentValues, mCurrency);

Some references

http://stackoverflow.com/questions/5483672/how-does-the-linq-refreshmode-work
http://stackoverflow.com/questions/6254220/what-is-the-correct-usage-of-datacontext-refresh