Signal source block periodic phase deviation problem

[Engin Karabulut]

Hi everyone,

I am running a simple flowgraph where signal source block generates sine 
wave and time sink shows waveform. Sample rate is 100 Msps and carrier 
frequency is 1 MHz.


But phase of signal deviates periodically, you can see from link given 
below.

https://streamable.com/pil3ma

Is there any way to circumvent this? Like changing a variable from inside 
a block?