I can confirm your observation.

Strange indeed.

It is well known that the Split Measure plug-in refuses to work with independent Time Signatures.

But you would not expect problems with independent Key Signatures.

You should inform the folks at MakeMusic about this.

Meanwhile, as a workaround, you can de-select independent Key Signatures, run the Split Measure plug-in, and then re-create the independent Key Signatures.

Thank you Peter
I solved my problem like you said "de-select independent Key Signatures, run the Split Measure plug-in, and then re-create the independent Key Signatures".

I need some help with measure splitting - i need split long measure more than one and i just don't know how to do this.

… I need some help with measure splitting - I need split long measure more than one and i just don't know how to do this …

Perhaps I do not understand.

When I need to split a measure into three “measure parts”, I just use the plug-in twice.

Example:

Time signature 6/4, need to split one measure into three “parts” of 2/4.

1) Select the last four Quarters, and run the plug-in.

2) Select that last two Quarters, and run the plug-in.

FYI:

The plug-in actually splits the measure into two real measures where the last measure is not included in Measure Numbering.