What version of LR5 are you running (latest is 5.7.1)? What version of OS X? Do you use a external display?
I am running Lr 5.7.1 on Mavericks (10.9.5) and cannot replicate what I think you are explaining.
Edit: On Mac Book Pro (Mid 2011).
Thanks for the quick reply.
OS X Yosemite (10.10.2)
I'm not using an external display. If it matters my MacBook is a 13".
As an example of what I mean, look at the image below. Everything highlighted in green I'm able to click. After I'm in develop for more than a few minutes, I'm suddenly not able to right click or left click on anything. The typical "mouseover" changes don't happen either, such as the subtly highlighting that happens when you mouse over an image in the bottom pain. As if Lightroom isn't detecting the mouse there at all.
Weird, never seen something like it.
Do you mean to say that you cannot click with the trackpad on anything on the left and right panels (e.g., Navigator, Presets, ..., Basic, Tone Curve)? I'll take the trackpad works fine outside Lr. What type of Lr license you have perpetual or a CC subscription?