I did not see your edit. If you did a layers to image size good chance the text is not text anymore, but I will post anyway
It really does help if you give OS and version of Gimp. Gimp 2.10 has a slightly different way of implementing textboxes, however as a guess it goes something like this.
1. Text can be in a dynamic (even dymamic ) text box or a fixed text box. You can swap from one to the other using the pop-up menu.
2. With fixed text box and the text tool active, click in it and whatever layer you are on, you switch to the text layer for editing.
3. Click outside with text tool active and a new text layer is created.
How to get round it.
The obvious, if a fixed text box is largely empty, reduce the size with the handles or make it dynamic.
If you have a fixed text box that is completely full or you want text over the top then try the old use editor option.
Start a new text layer, even if it is off the canvas, enter the text in the editor, then move the text layer into required position.
With text tool active ctrl-alt click-n-drag moves text otherwise move a text layer using the move tool with move active layer enabled.
It really does help if you give OS and version of Gimp. Gimp 2.10 has a slightly different way of implementing textboxes, however as a guess it goes something like this.
1. Text can be in a dynamic (even dymamic ) text box or a fixed text box. You can swap from one to the other using the pop-up menu.
2. With fixed text box and the text tool active, click in it and whatever layer you are on, you switch to the text layer for editing.
3. Click outside with text tool active and a new text layer is created.
How to get round it.
The obvious, if a fixed text box is largely empty, reduce the size with the handles or make it dynamic.
If you have a fixed text box that is completely full or you want text over the top then try the old use editor option.
Start a new text layer, even if it is off the canvas, enter the text in the editor, then move the text layer into required position.
With text tool active ctrl-alt click-n-drag moves text otherwise move a text layer using the move tool with move active layer enabled.