This seems to be a feature of the T-device in SPICE. At O-device (Lossy Transmission Line) and T-device (Lossless Transmission Line) modelling issues - LTwiki-Wiki for LTspice it is mentioned that “there is no dc connection between the input pins and the output pins (this is why both ends must have a path to ground).” If there is no path to ground, the dc voltage at the output is undefined and may take an arbitrary value.