Framerate drop when looking at panels?

I've recently installed Portal 2 on my Ubuntu partition, and I've noticed an interesting issue that has popped up while playing community test chambers, but it has also surfaced around the beginning of story mode Chapter 1. I can usually get upwards of 60-70 FPS based on my graphics settings, but whenever I look at a movable panel, my frame rate drops severely, usually to below 30 FPS. My specs are as follows:
Ubuntu 14.04 LTS
Kernel version 3.18.0-031800-generic
Intel Core i5-4200U (2 physical cores, 4 total logical cores)
Intel HD Graphics 4400 iGPU (Driver: Intel Corporation Haswell-ULT Integrated Graphics Controller version 09)
(Note: The driver version number is according to the output of
sudo lshw -C video
)
And my Portal 2 video settings are:
Aspect ratio: 16:9
Resolution: 1366 x 768 (Native)
Display mode: Full screen
Laptop power savings: Disabled
Splitscreen direction: Default
Anti-Aliasing: None
Filtering mode: Trilinear
Wait for Vertical Sync: Disabled
Multicore Rendering: Enabled
Shader Detail: Low
Effect Detail: High
Model/Texture Detail: Low
Is there anything I can do to fix this issue? I'm still able to play normally, but the FPS drops catch me off-guard and can get annoying.
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Why does my framerate randomly drop?
FPS drops can occur if you have problems with your connection or the servers are too busy, while system configuration is also very important. To start resolving these issues, you will first need to check if everything is running optimally, and then gradually move onto updating drivers.How do I stop frame rate dropping?
How to Stop Dropped Frames in OBSHow To Fix Windows 10 FPS Drop Fix for Gaming
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Images: Khoa Võ, Анастасия Беккер, cottonbro, Klaus Nielsen