As reported here, the Text Editor uses the incorrect theme color for text lines if syntax highlighting is OFF but line numbers are ON.
This can be seen easily if you change the line number and text colors a bit. In the middle of the following you will see that regular text lines (except for current line) are drawn in the line number color:
In a nutshell the code was changing the text color to draw the line numbers but was not cleaning up after itself and changing the color back. After this patch is applied it works correctly in all three variations:

