spindle.0.at-speed and s decrease problem.

I'm configuring vfd via modbus and I encountered a strange problem. 
My hal configuration is correct, I suppose, the problem is rather in LinuxCNC.
LinuxCNC should wait for spindle.0.at-speed = 1 before making a G1 move, and it waits after the spindle starts, but it doesn't wait after the speed changes.
My English is not good, so instead of explaining, I will give an example. Machine waits after m3s24000, but not waits after s2400.
But code bellow works as expected. The only difference is one milisecond dwell...
Do I something wrong, or it is a bug ?

Temporary solution:
1. Add to your ini file line bellow in [RS274NGC] section: 2. Make and place in proper folder setspeed.ngc file: Now LinuxCNC waits at every change of spindle speed.
Tested by code bellow: