Date/Patch of first occurence: [RF]
When using the combo start skill or a skill inside the combo chain it can happen that the combo does break. This happens when the MP of the players reaches zero and a MP potion needs to be consumed. The issue is related to latency. When the ping is lower than a certain (unknown) limit the MP potion will be consumed and the combo continues. Installing Letrix3 from http://www.leatrix.com can reduce the effect. On very rare occasions the combo will even break if the amount of MP is sufficient.
The Issue was not visible before the Rising Force patch, probably some timing was changed there. The client seems to not accept some additional latency now.
How to reproduce: Use a skill in combo while the MP for the use is not available while the connection responds slow.
Currently investigating the issue deeper.