When editing a previously entered signal producer's input string the previous input can be shown as an invalid input string. This means that, when this bug actually occurs, clicking Configure on the already configured signal producer and then immediately Confirm makes the signal producer become null as its input is no longer valid (and hence lost).
Below are invalid transformation cases I have most certainly seen. Note that they are consistently shortened forms that still carry the original data, but with placeholders and separators removed.
P-------becamePCu------becameCucrcrcrcr:WuWuWuWu:WuWuWuWu:WuWuWuWubecamecrcrcrcrWuWuWuWuWuWuWuWuWuWuWuWu
This bug is very inconsistent. I never manage to reproduce it, alas, but it definitely occurs. I think I've only seen this on copied signal producer: the original signal producer already had a value set, editing the copy for the first time then shows the invalid, shortened value. Editing another copy has so far not reproduced this, nor editing the same copy, nor another signal producer from the same copy action (e.g. when copying four already configured signal producers in one action). I've even come to suspect this happens only the first time in a game session?