On the VStar forum, Avon reports:
"I have been trying to use the equation given from Vstar to overplot the data with the model light-curve using a programming language (for research purposes).
However, I find that using the given equation, with the dates of the data, often does not match the fit in the Vstar plot itself, there is a offset in the phase, such that the model curve (despite being correct in period and amplitude) does not fit the data. I have experimented with this but can see no obvious reason."
The zero point from the model creation was not being included in the model function strings in the ModelInfo dialog.
Fixed in https://sourceforge.net/p/vstar/code/962/
Fixed in 2.15.1