It seems like the state of the textbox is saved even though the user presses "Cancel" in the options.
Steps to reproduce:
1. open ThinLinc client options
2. check the "Start the following program"-checkbox
3. close the options by pressing "OK"
4. open the options again
5. uncheck the checkbox
6. close the options by pressing "Cancel"
7. open the options again
8. checkbox is now checked but the textbox is disabled
Fixed in commit 29063.
Works well now.