Incorrect behavior of an element with a CMD tool when full path is not specified

A simple element with a CMD tool was created.
The execution string was the following: "python C:\TEST\test.py $in $out".

The schema was:
"Read sequence" > the element > "Write sequence"

The schema ran successfully, but the output file was not produced!

When the execution string was modified to "C:\Python27\python C:\TEST\test.py $in $out", the schema ran as expected.