I have followed the scenario you described, and still the issue does not reproduce. Here's what I did
1. Create a master page with 3 content placeholders
2. Create a template in Sitefinity, called "master" that's using the master page as template
3. Create a template in Sitefinity called "inner" based on "master"
4. Inside "inner" I have the 3 placeholders by default. I have placed a layout element in one of them and placed the TabStripTest control (the one I have shown you in a video form the there thread you had open on this topic).
5. For the sake of complete testing I have also tried these scenarios:
a) TabStripTest placed outside of the placeholders
b) TabStripTest placed in a layout element added to the "inner" template
In all the above scenarios the control is showing up in both design, preview, and live mode. I have also experimented with having multiple instances of the control on my page, which all worked fine (tab switching)/ Please let me know if the steps I've taken differ from what I've done, please let me know, so I can inspect this issue further.
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