I've reproduced the bug.
The problem is that on switching to the datamanager, the measurement is still selected in the render window, but the measurement value disappears.
After switching to the datamanager, the same measurement can't be selected again.

I think the measurement should be unselected by switching to
the datamanager. So the measurement and the measurement value will be
unselected instead of selecting the measurement and still display the value.

New remote branch pushed: bug-16600-UnselectingMeasurementByClickingOnDatamanager

[a3183d]: Merge branch 'bug-16600-UnselectingMeasurementByClickingOnDatamanager'

Merged commits:

2014-01-29 16:36:00 Silvio Kolb [91b8a0]
Changed iteration over all datanodes and casting
them to iteration over a subset of datanodes that are planarfigures

2014-01-29 13:52:32 Silvio Kolb [c6c686]
cosmetical changes

2014-01-22 17:08:03 Silvio Kolb [2c340d]
Deselecting all planar figures if none is selected and clicked on datamanager

To reproduce this error perform the following steps:

1. select the line tool
2. select another line in the data manager (this is not a common workflow but possible)
3. draw the line

> now the line is drawn in white and the previously selected line is drawn in red

Tested on Linux