Multiplexed messages must not contain empty sub-messages. This is errorprone and useless. To fix this:
1) Eliminate the "If empty input" parameter from the element.
2) When the "1 to 1" multiplexing rule is selected, the element must produce the multiplexed messages only while BOTH elements have some messages left.
So, let the first element has N messages, the second element has M messages. You should test at least the following scenarios.
- N > M - there must be M multiplexed messages
- N = M
- N < M - there must be N multiplexed messages
3) Remove the "Many to 1" value of the "Multiplexing rule" parameter. It is redundant and, therefore may confuse a user even more. and if a user wants to switch the first and the second input ports he/she can delete the connecting arrows and connect the elements to the opposite ports.
4) "1 to 1" and "1 to many" is not translated for some reason. If you translate them correctly, modify Russian translation of input ports also, as they contain mentioning of the values.
5) Don't forget to update English and Russian translations, e.g. remove the obsolete ones.