Short answer is that yes, you can have an implement that is labeled QH compatible and still have issues. In my opinion the only sure fire way to beat that problem is stick with one brand of QH and implement. For instance my Harbor Freight QH didn稚 like my Land Pride QH compatible brush hog without a top link adapter and lower link bushings. Ultimately, it was even more of a pain to hook up with the HF QH because it was harder to access the PTO shaft. Since I have all different makes and ages of implements I ended up welding on euro style hooks. I have had them on for several months and I値l never have another tractor without them. They are essentially a heavier duty and standardized hook like the Pats system.
This ^
I had some steel plates fabricated in an attempt to make an old blade scraper compatible with my Kubota QH15 and it turned out to be more of a hassle than just taking the QH off.
The idea of a QH is great if everything works like it should. I love it when switching from my carry-all* to my box scraper, but am now looking for a replacement scraper blade.
* Note: My TSC carry-all frame needed some 'spacer' 2X4's between the frame and carry-all platform to provide enough space for the bottom hooks on my QH15 - a modification that some other brands of carry-all frames don't require.
So yeah, QH system can be a hassle but I think they're worth it once you get past that phase.