My wife has the Topeak QuickTrack system on her bike. She recently bought the Topeak MTX rear basket that works with the system, however, the geometry of the bike seat and basket are such that she couldn't slide the basket far enough forward to engage the latch without hitting the back of the seat. Apparently, based on internet comments, this is a fairly common problem.
My solution? Re-engineer the latch to give some extra space. I used Sketchup to create a 3D model (available here on Thingiverse) that solved the problem for my wife's bike, and printed it on my 3D printer. I thought I would share it here in case it would be helpful to someone else in a similar situation. Leave a comment below if you have a question about it, or a suggestion for improving the design.