I've been working on and off with Inkscape on an electric schematic for the last 3 years. The size of most of the lettering cannot be changed, which is quite annoying. I select, say a text with 8pt, mark it (the colour changes), I select a new size - say 10pt - and nothing changes in the drawing. If I select the same text again, it says incorrectly it is 10pt. If I make a new lettering, I can change the size without problems. What do I have to do to change the size of my old lettering? It would take me quite some time to rewrite all the lettering.

Maybe you have seen this: http://wiki.inkscape.org/wiki/index.php ... /0.92#Text

Text was changed in 0.92x. ( and may be revised again).

Can you see the code for the text objects and investigate the difference that is blocking it?

Edit > XML Editor (Ctrl + Shift + X).

Or if you can let us see the SVG file.