When printing a pdf, the drop down icon is sometimes visible

Good evening, 

we are using the free Adobe acrobat reader DC version and have seen a curious phenomrnon.

For school regulations we have to fill out several pdf formular with some drop down menu bars. 
When we try to print these documents, sometimes the drop down icons is shown on the paper and sometimes not.

Does anyone know, why? And where we can manage it?

Thx Bjoern