Here are all important links:
viewtopic.php?f=1&t=4740
-A few rules and useful forum instructions
That is odd
please post your:
* Name of your Operative System (Windows/ Linux/ Mac) And subtype ('Home' 'Mint' '10.13' aso)
* lmms version
* lmms sound device chosen
* hardware specification (ram & soundcard is the most important)
* link to a copy of that midi-file