Program crash when opacity of base layer changed

crh2pw[CodePlex]
If I try to type in a new opacity for the online base layer in the opacity drop-down, after I type and click enter, the program crashes. The problem does not happen if I select opacity from the drop-down menu, only when I try to type in a value and click
enter. This is reproducible. I tried doing it 3 times with the same crash.

Start by reproducing the crash in the Windows application using the online base layer's opacity field: type a value and press Enter, rather than selecting a dropdown value. Trace the opacity input handling from that interaction and confirm the application no longer crashes; add or update a regression test if the project provides coverage for this UI behavior.

Written by the indexing model from the issue text.