Non-critical Stage 3 bug

This is not a critical issue, but I'm reporting it just in case.
I'll describe a bug I encountered while replaying the campaign to complete the remaining tags and challenges.
The issue occurred when I cleared stages 1-3 on Beginner difficulty. 
The game froze on the final screen of stage 3. 
I could press ESC, but I had to exit through the options menu.
Details are as follows:
1. I collected all tags in Stage 1 except the first one and advanced to the next stage. I also achieved a knife kill during this stage.
2. I collected the two outdoor tags in Stage 2 and advanced to the next stage. I also achieved the no-death challenge during this stage.
3. Collected all tags in Stage 3. Aiming for the Handgun Challenge, I used only handguns except for destroying the first mortar with an RPG. Left the tank to allies.
4. The game froze on the same screen at the end of Stage 3.