Placed dimension disappears

I place a new dimension with the following sequence:

Pick up dimension linear command

select start of dimension: give data point on corner of first object

select dim endpt: give data pt on cnr 2nd object

define length of xtn line: give 3rd data pt

place dim text 4th data pt

select dim endpt right click for reset (left button is data pt, centre is tentative, right is reset)

select dim endpt:  pick powerselector in popped up menu

give data point in empty space

dimension, which was fully formed, just disappears.

all the above I do so fast it happens without any thinking, and the end I have nothing.

this has happend to me hundreds of times.

then, i will repeat exactly the same sequence, and it works. the dimension does not

disappear.

if reset exits the command, why would the dimension disappear?

thanks for any help

Jim