problem with moving objects and distance

[coek]

We are using AutoCAD 2004 mechanical
When you select lines in the TRIM / EXTEND command,
and you have to select more then one line,
while you click of them, they do not trim (or extend) at that moment.
For result you have to complete the command with "ENTER"
So you have to remember which lines you already selected,
and which you didn't.

We have the same problem for the "MATCH PROPERTIES" command.
Remarkable is that this problem only happens occasionally.

Could anyone give advise of this problem?