Steps to reproduce:

1. Create a new calculated item
2. Try to last() function to get another host key value with a user macro as a host parameter.

Result:
See screenshot...
Try the get the value without a user macro as a host parameter works as expected, but not with the user macro:

Works: 

last(/myHost/oltPonTxOpticalPower.[472907776])

Don't work: 

last(/{$MYHOST}/oltPonTxOpticalPower.[472907776])

Expected:
Get the value of the key with a user macro as a host parameter.