multipule touch issue

Hi, all:
our APP made with unity(5.6.0), we need to scale the model by two fingers. And also we need to take a picture by calling image picker.
However, once we did took a photo then we can't scale the model cuz APP can only detected first touch.
The state of multipletouchenabled is true.

Here is the flow:
we scale the model by two fingers ------- works fine.
take photo ---- get the texture data;
we scale the model by two fingers ----- Only can detect first touch, seems like...

multipule touch issue