kernel panics - thunderbolt+TV+sleep

Hello,

I am getting black screen with note in a few languages that my computer restarted due to a problem...it is macbook air 13 early 2014, yosemite 10.10.3, 1,4 GHz Intel Core i5, 4 GB 1600 MHz DDR3, Intel HD Graphics 5000 1536 MB.

As far as I could observe the thing, it happens only when MBA is connected through thunderbolt to a TV when watching movies or so and it stays connected to TV and a external HDD and fall asleep. When i open the lid I found the a.m. error on the screen or today I even had to log in with password. It happened a week ago, so I called to support, probably US(I am from SLovakia). The guy advised to update to El Cap, which I do not want to. We also went to Library and deleted Cashes. As the problem did not occur for a week, even if I tried to simulate the problem with thunderbolt+TV+ext HDD situation, I thought deleting cashes could help. the restart did not occured till today, twice.

any idea how can I fix it? It is in warranty, so I am considering to send it back to iStore.

cannot paste error details which can be sent to Apple, it says: The message contains invalid characters.

Thank you

Martin