PageCount++ GuiControl,, TabControl, Page %PageCount%
According to the documentation of GuiControl, the code above should create a new tab "to be appended at the end of the control's list."
Instead, it does the exact opposite. It adds a new tab with the given name to the beginning of the controls existing list. Even worse though is that, due to the way tabs work, the leftmost tab (the newly created one) still contains the content of the previously leftmost tab. The effect of this is that everything appears to shift down one tab, so that the old rightmost tab (still with its old name) has the contents of the newly created tab.
I am hoping that I am doing something wrong, or that there is some easy way to fix this incredibly strange behavior.