Thermal analysis in Optistruct - Gap elements

Hi,
I have a problem with heat transfer in Optistruct - I have  solid elements connected with shell elements using Gap elements, heat source is temperature on solid elements and there is two cases:
1. gap elements work properly when there is only conduction heat transfer between those two components

2. gap elements do not work properly when I add convection between ambient and shell elements.

Do anyone have an idea what is wrong and could help me solve this issue?