UNIQUE[] without parameters gives error

#1
With v17, when I use

[C:\Program Files\JPSoft\TCMD17x64]echo %@unique[]
TCC: (Sys) The parameter is incorrect.
""

yet with v16, I get the expected temporary filename.

The solution was to give it a PATH

[C:\Program Files\JPSoft\TCMD17x64]echo %@unique[c:\temp]
C:\temp\UNI5505.tmp

Not sure what is going on here; a batch file became ornery. The "What's New" states that UNIQUE had been updated.