VCO veriloga behavior modeling question

[filtershaoyong]

verilog-a

I use the kundert's VCO modeling and find some problen when do simulation in Hspice.

The problems: the VCO works well under 10uS, but the output is wrong when tran simulation larger than 10uS.

I don't know what's wrong?

you can get the result use attachment hspice netlist.

Thanks,