I had a similar problem. I use Kubuntu and I was working with the 6.10 version. No problem with QCad 220.127.116.11 Community Edition. But recently I upgraded to the actual version (7.04). QCad was upgraded too, from Aug 12 2006 to Nov 10 2006 and the same version number for both: 18.104.22.168. In the upgraded version, if you do a circle with a radius of 5 units, no problem, but if you want a radius of 5.5 units, nothing was drawn. Now I think a circle of zero radius was drawn.
Another problem was insert blocks that I drew before I upgraded. In first place, when I insert a external block, from the libraries directory, nothing was drawn, but the name of the block and the layer that this block inserts appears in the lists. The solution was to change the factor to a value distinct of 1.0 and after a insertion go back to 1.0. This solved the problem, but the lines weren't vertical or horizontally, and the size of the text changed too. I normally use 2.5, 3.5 and 5 mm as text size. The text were transformed to 2, 3 and 5.
I searched with the packet manager (adept) for scim-qtimm, and yes, this packet was installed in the upgrade. So I removed it, and now seems work right. I removed this packet in the 6.10 version, because I had similar problems with scribus. My locale is Galician (Spain) gl_ES.