Setup:
Create template A that is in two host groups (G1 and G2).
Create template B that is in host group G1.

Reproduce:
Export template A and B in JSON format.

Notice:
template A export

...
"groups":{"1":{"name":"G2"},"0":{"name":"G1"}}
...

template B export

...
"groups":[{"name":"G1"}]
...

Template A is exported incorrectly groups should be in array.