Help wanted for layers and pagebackgrounds

[Otared Kavian <otared@gmail.com>]

Dear all,

I need to have a special layout, in which a number (which is not a page number nor a section number or such) is printed in big size on the right when the pagenumber is even (that is on a leftpage) and printed on the left when the pagenumber is odd (that is a rightpage). With the help of examples gleaned here and there in the manuals, I came up with the following minimal example:

%%%% begin
\setupcolors[state=start]
\setuppagenumbering[location=footer,alternative=doublesided]

\definelayer[NumberRight][width=\paperwidth,height=\paperheight]  
\definelayer[NumberLeft][width=\paperwidth,height=\paperheight] 

%\showframe
\define[1]\myNumber{%
	 \setlayer[NumberRight][preset=righttop,voffset=45mm,hoffset=3mm,reset] % without reset the problem is the same
		 {\offset[location=rt,rightoffset=-3mm]
		    {\tlap{\startcolor[darkgreen] 
					\switchtobodyfont[ss]
					\scale[height=30mm,width=22mm]{#1} 
				\stopcolor}
			}
		 }
		\setlayer[NumberLeft][preset=lefttop,voffset=45mm,hoffset=25mm,reset] % without reset the problem is the same
		 {\offset[location=tl,leftoffset=-3mm]
		    {\tlap{\startcolor[darkgreen] 
					\switchtobodyfont[ss]
					\scale[height=30mm,width=22mm]{#1}
				\stopcolor}
			}
		 }
	}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Maybe the problem is here?
\setupbackgrounds[leftpage] [background=NumberRight] 
\setupbackgrounds[rightpage][background=NumberLeft]
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\starttext
\dorecurse{4}{\myNumber{#1}\input knuth.tex \page}
\dorecurse{4}{\myNumber{#1}\dorecurse{5}{\input knuth.tex }\page}
\stoptext
%%%%% end 

The problem is that in some cases (for instance on pages 2, 3, 4 of the above example) the big numbers are overprinted.
In particular the behavior seems not to be the same on all pages, that is after the two \dorecurse above.
I guess my lack of knowledge in using and setting layers is the cause, but can anyone tell me please what am I doing wrong?
This problem arises in a document in which I have to use mkiv, but in mkii one ha the same result.

Thanks in advance and best regards: OK
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