Wow, there's a lot of attitute in this thread. The very nature of the locking mechanism on liner-locks or framelocks dictates that a perfect lock-up is on the verge of being sticky, and also on the verge of being sloppy. Titanium itself is a softer metal than the tang of any knife, and is prone to galling. Which means that it does some interesting things when it is jammed up against a harder material.
The entire construction of the lock bar, lock bend and tang interface is critical to how the knife works, breaks-in, and holds up over time. Having built 1000+ knives of this style, I believe I am fairly competent to speak on this topic. Assuming the geometry selected by the knifemaker is correct (and this is not always the case), removing as little as 0.0002" from the tang can change the lock-up of a given knife. I know this because I grind my tangs on a fixture that uses a micrometer to control the amount of metal removed and I am able to make adjustments as small a 0.0001" during this operation.
If you have any idea of how small 0.0001" is, you should be able to comprehend that even a minor high spot (virtually unnoticeable to the eye, even with magnification) on the end of the lock-bar can cause a sticky lock. This is where the Sharpie comes in. The Sharpie provides enough lubrication to let the high spots on the lock-bar conform to the surface of the tang (which also is not perfect). It prevents galling, where the condition of the face of the locking bar would become rougher and more uneven, making the sticky lock even worse.
As to the gentle spine whack, it is actually a two step process and is fundamentally sound in its Engineering. The knife (before sharpening) is first opened and the edge of the blade is first tapped firmly on the workbench several times. This seats the stop pin and internal components at their "Maximum Material Condition" (MMC) If you don't know what MMC is, either do some research or trust me. <G>. It's the condition where all the parts of the knife cannot shift in a direction that would change the lock-up. (stop pin seated rearward, pivot pin seated fully forward).
Once the parts are seated, and the preliminary lock-up is eatablished, a GENTLE spine whack (knife tapped on the bench upside down) will mate the tang surface to the end of the lock-bar perfectly. If the lock is still sticky, the knife is disassembled and more material is removed from the tang. The process is repeated until the lock-up is correct.
This procedure is performed on EVERY knife made at KERSHAW, BTW, and their locks are the best in the business, IMO. Their locking bars are generally Stainless steel, and they really whack them hard. With Titanium and the Sharpie marker, I have found that a gentle tap or two is sufficient.
Of course, the spine tap will also point out bad geometry, as the lock will be defeated (slip) if the geometry is not good. With correct geometry, the lock will actually seat itself more fuly or remain un-changed.
Hope this helps. Of course, on a custom, there is nothing wrong with contacting the maker and asking him to address the problem. It's just that often, the "Sharpie Trick" will correct it.
Just my 2 cents.
Have you ever owned a titanium framelock?
back for the same problem, got a new one (to my likings & specs) that works great even if opened very hard