Long story short, Blink is a long way from 100% reliability. It's still dang useful, but it ticks me off every time it fails.
I propose the following minor glyph, which should fix this issue:
Glyph of Blink to Location: Causes your Blink spell to teleport you to a targeted location.
Simple, is it not? Granted, it adds an extra click to its use, but that's why it's a glyph; this makes it optional for people that like it as-is. The check for a valid targeted location is different and more flexible than the check Blink currently makes. That check also happens before cast, so instead of wasting the cooldown (and the GCD) doing nothing, nothing happens, and Blink remains off cooldown.
It wouldn't add to Blink's range; you would still only be able to blink to a place within 20 (25 with the Major Glyph of Blink) yards. It also shouldn't make blinking to non-frontal locations faster; theoretically, it would take just as long to click on the location behind you to blink to as it would to turn around and blink.