Dragons leaving their Own habitats

[lovenpis]

Hello everyone! I got a problem with my dragons... They are leaving their Own habitats without doing anything. I don't sell or trade or do anything and when i leave and Come back i got some dragons left... I don t know what to do . I let a mail to the team... Is it ever happened to anyone ? What CAN i do ? Are they left forever ? Thanks for answers .
Lovenpis