Issues on saving Units with a lot of Unit Pages

We found a big issue on CoursePress Units with a lot of Unit Pages, more than 15. When saving Units, sometimes it doesn't save all the Units and sometimes it does not save the whole Unit, ending up with a blank Unit after saving.

Here's some screenshot to better explain:

Current number of Unit Pages is 20 BEFORE saving:
http://i.imgur.com/oHOraD4.jpg

Current number of Unit Pages is 18 AFTER saving: http://i.imgur.com/u8bXis2.jpg

As you can see in the screenshots, we have 20 Units before saving. We pressed the Save button and after the page reloads, Unit 19 and Unit 20 wasn't saved.

Another issue was when we press the Preview button, instead of opening a new tab with the preview of the Unit page, a new tab with the Unit editor opens and it seems the Unit was saved (as if pressing the Save button): http://i.imgur.com/vcQSyAG.jpg

I extended Support Access just in case you need to access the backend.