About the multiple files, I had this problem too, BUT I found out how to stop it.
About the single files, I have not had this problem, and of course not found out how to stop it.
To fix the multiple files, just rename you frames, "Frame_0" "Frame_1" "Frame_2" "Frame_3" etc...
The word frame in the examples stands for your object name. Always remember to start at 0. This should fix it.