Inkscape V0.91 Problem (with "opacity") Printing To PDF - Black Page

If anyone else uses the vector graphics programme "Inkscape" for workshop stuff, you may have a problem printing to PDF which might just be very elusive to solve.
If it prints to PDF with the page black, go searching in your drawing for an "object" with a degree of "opacity" other than 100%.
Either use 100% opacity or delete the object.the
It appears that there might be a problem with PDF interpreting the opacity info.

If you cannot find any suspect objects, save your work, save as a "temp", and within "temp" delete layer by layer until you solve it.
If you only have one layer, delete objects until problem is fixed.
You may even have a tiny dot, eg an M3 screw hole, with less than 100%.
This may have occurred when you change opacity in overlaying a rough hand drawn layout drawing with an underlying front panel etc, or merging two photos of layouts.

Apparently this problem will be fixed in the next stable version.
And probably everyone knows about this except me.

Very good programme, after you learn it, and the price is right, free.
I use it for project panel layouts, electronics equipment dials and for drilling templates etc.

cheerio