Why MaestroSBT changes subtitle times when i do conversion .son to .ssa ?

Example:

SSA from Sub Station Alpha looks like this:

First Line in subtitles:
Dialogue: Marked=0,0:00:23.02,0:00:26.69,*Default,NTP,0000,0000,0000,

Last Line in subtitles
Dialogue: Marked=0,1:49:21.52,1:49:23.19,*Default,NTP,0000,0000,0000,

Then i convert .ssa to .son with MaestroSBT and .son file looks like this

First line:

0001 00:00:23:00 00:00:26:20 movie-1_0001.bmp

And last:

1332 01:49:21:15 01:49:23:05 movie-1_1332.bmp



when the subtitle file is .ssa syncs great, but when i convert it, then it is not in sync anymore. What is the problem ?

Movie is 29.97 and subtitles also is for 29.97, and i have been tested all compinations in MaestroSBT timings (i think?)