I believe this is not a bug. E is a projectile. So it has a travel time, and where you placed that Q... your E has already passed through before Q can materialize and be affected by your E.
The closer+earlier you use your Q, the more longer you need to wait use your E effectively. There's a point (you passed that point in this video) where you cannot use your Q then E in that given moment. After using your Q in melee range, you need to wait for a few milliseconds before using E.
TIP: Experiment with Syndra by entering the Practice Tool mode.
This is a common occurence among Syndras that panics against champions that surprises Syndras in melee range. It can be avoided a lot by reading the situations beforehand. Panicking in a game is usually forbidden, not good ping. It's important to understand the mechanic, your champions, and stay calm in situations like these.
Did you know at a range, max range for example, you can use E first, then Q to stun an enemy as well? Did you know you can extend the ball's travel range (under effect of E) up to 1.99x (this is an approximation) the range? I admit, this one is under specific conditions.
If not, you still have things to learn and get the "feel" of Syndra ^.^!
-Syndra main
