Certain specific conditions can trigger malfunctions in the Marketplace My Content section. The malfunctions are triggered when you view the My Content page and select a category (e.g. Add-Ons) in which the number of items listed fits within a single page, so that the list is presented without a scroll bar. Once triggered, two malfunctions start happening:

1. The laying out of slots in the output list starts out as expected, but soon intermediate rows are not being filled, and eventually new items are only being inserted into slots that have already scrolled off the top of the viewport. This problem can be easily corrected by selecting a different category that has enough items to need a scrolling list.
2. While still in My Content after the trigger, if you press the Marketplace button (the top button above My Content), nothing happens. The "<" (Back) button still works, however. This problem is not as easy to correct: You have to go back to the game's title page.

Steps to reproduce:
Requires an account that owns a small number of Marketplace items in at least one category (Add-Ons, Skins, Worlds, Textures, or Mash-ups) and at least a dozen or so items in at least one other category.

1. On the game's title page, press the Marketplace button.
2. On the Marketplace main page, press the My Content button (on the left, 2nd from the top).
3. Click a category with just a few items, so that the list presented has no scroll bar.
4. Click a category with many items, so that the list has a scroll bar.
5. Scroll through the list and notice how it fills as you get farther down.
6. Click the Marketplace button at the top left.

Observed results:
In step 5, after a few normal rows, new rows are no longer filled and subsequent rows are filled less and less until all the new rows are empty.
In step 6, the button is ignored.

Expected results:
In step 5, the lists are filled left to right and top to bottom in the normal way.
In step 6, the button always returns you to the main Marketplace page.

Analysis and Additional Information:

For the scrolling behavior, I believe what's happening is that the presence or absence of the scroll bar in the item list causes two different values to be calculated for (depending on how the algorithm actually works) either the number of item slots that can fit in a list row, or the width of an item slot. There may also, or alternatively, be a rounding error in this value. It could also be a problem with the timing of this calculation, because it appears that each category's list uses the value that would have been appropriate for the previously selected category, as if the previous stored value is fetched before the newly calculated value is saved. (I make no attempt to explain what happens for the first category selected.)

For the inoperative button, I don't have a clue how that might be related to the scroll bar absence or presence.

I first saw this problem long ago, probably when My Content was introduced, but I didn't discover how to reproduce it reliably until now.